diff --git a/lecture_4/homework/app/controllers/clans/warriors_controller.rb b/lecture_4/homework/app/controllers/clans/warriors_controller.rb
index 6ccf3ff9..acab2d6a 100644
--- a/lecture_4/homework/app/controllers/clans/warriors_controller.rb
+++ b/lecture_4/homework/app/controllers/clans/warriors_controller.rb
@@ -10,7 +10,7 @@ def index
       warriors = clan.warriors
 
       if params.key?(:alive)
-        if params[:alive].to_i == 0
+        if params[:alive].to_i.zero?
           render json: warriors.dead
         else
           render json: warriors.alive
diff --git a/lecture_4/homework/app/controllers/mercenaries_controller.rb b/lecture_4/homework/app/controllers/mercenaries_controller.rb
index 4382cfcf..d1206231 100644
--- a/lecture_4/homework/app/controllers/mercenaries_controller.rb
+++ b/lecture_4/homework/app/controllers/mercenaries_controller.rb
@@ -3,7 +3,7 @@
 # This controller is written badly on purpose. Please refactor this
 class MercenariesController < ApplicationController
   def index
-    render json: Mercenary.where('available_from < ?', Time.now).all
+    render json: Mercenary.available
   end
 
   def show
@@ -11,17 +11,14 @@ def show
   end
 
   def employ_best
-    mercenary = Mercenary.where('available_from < ?', Time.now).order(price: :asc).first # TODO: what about experience?
-    clan = find_clan
-    building = find_building
-    warrior_class = clan.warriors.select('type, count(type) as warriors_count').group(:type).order('warriors_count ASC').first.class
-    warrior = warrior_class.create!(name: mercenary.name, clan: clan, building: building, preferred_weapon_kind: mercenary.preferred_weapon_kind, mercenary: mercenary)
-    create_good_weapon(mercenary)
+    mercenary = best
+    warrior = WarriorRecruiter.new(mercenary: mercenary, params: mercenary_params).call
     render json: warrior, include: [:mercenary], status: 201
   end
 
   def employ
     return unless mercenary.available_from < Time.now
+
     clan = find_clan
     building = find_building
     warrior_class = clan.warriors.select('type, count(type) as warriors_count').group(:type).order('warriors_count ASC').first.class
@@ -37,9 +34,7 @@ def mercenary
   end
 
   def find_building
-    if params[:building_id]
-      Building.find(params[:building_id])
-    end
+    Building.find(params[:building_id]) if params[:building_id]
   end
 
   def find_clan
@@ -50,14 +45,11 @@ def find_clan
     end
   end
 
-  def create_good_weapon(mercenary)
-    case mercenary.preferred_weapon_kind
-    when :melee
-      Weapons::Katana.create!(warrior: mercenary.warrior, range: 2, damage: 25)
-    when :ranged
-      Weapons::Musket.create!(warrior: mercenary.warrior, range: 40, damage: 10)
-    else
-      # TODO: some default?
-    end
+  def best
+    Mercenary.available.cheapest
+  end
+
+  def mercenary_params
+    params.permit(:building_id, :clan_id)
   end
 end
diff --git a/lecture_4/homework/app/models/mercenary.rb b/lecture_4/homework/app/models/mercenary.rb
index 82aa4bdd..6787ce14 100644
--- a/lecture_4/homework/app/models/mercenary.rb
+++ b/lecture_4/homework/app/models/mercenary.rb
@@ -11,6 +11,8 @@ class Mercenary < ApplicationRecord
 
   validates :warrior, uniqueness: { allow_nil: true }
 
+  scope :available, -> { MercenariesQuery.available }
+  scope :cheapest, -> { MercenariesQuery.cheapest }
   scope :alive, -> { where('death_date IS NULL') }
   scope :dead, -> { where('death_date IS NOT NULL') }
 end
diff --git a/lecture_4/homework/app/models/warriors/hussar.rb b/lecture_4/homework/app/models/warriors/hussar.rb
index c277ff70..0dee7137 100644
--- a/lecture_4/homework/app/models/warriors/hussar.rb
+++ b/lecture_4/homework/app/models/warriors/hussar.rb
@@ -5,7 +5,7 @@ class Hussar < Warrior
     attribute :preferred_weapon_kind, :string, default: :ranged
 
     def attack
-      "Hussar #{name} charged while yielding #{weapon.type.demodulize}"
+      "Hussar #{name} charged while yielding #{(weapon || NullWeapon.new).type.demodulize}"
     end
   end
 end
diff --git a/lecture_4/homework/app/models/warriors/samurai.rb b/lecture_4/homework/app/models/warriors/samurai.rb
index 2b477760..cd37cc06 100644
--- a/lecture_4/homework/app/models/warriors/samurai.rb
+++ b/lecture_4/homework/app/models/warriors/samurai.rb
@@ -5,7 +5,7 @@ class Samurai < Warrior
     attribute :preferred_weapon_kind, :string, default: :melee
 
     def attack
-      "Samurai #{name} attacked with #{weapon.type.demodulize}"
+      "Samurai #{name} attacked with #{(weapon || NullWeapon.new).type.demodulize}"
     end
   end
 end
diff --git a/lecture_4/homework/app/models/weapons/rod.rb b/lecture_4/homework/app/models/weapons/rod.rb
new file mode 100644
index 00000000..f330469a
--- /dev/null
+++ b/lecture_4/homework/app/models/weapons/rod.rb
@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+module Weapons
+  class Rod < Weapon
+    attribute :kind, :string, default: :magical
+
+    def calculate_damage(distance)
+      distance < range ? damage * 2 : damage / 2 + 42
+    end
+  end
+end
diff --git a/lecture_4/homework/app/null_objects/weapon.rb b/lecture_4/homework/app/null_objects/weapon.rb
new file mode 100644
index 00000000..c6a5c75c
--- /dev/null
+++ b/lecture_4/homework/app/null_objects/weapon.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class NullWeapon
+  def type
+    'Null Weapon'
+  end
+end
diff --git a/lecture_4/homework/app/queries/mercenaries_query.rb b/lecture_4/homework/app/queries/mercenaries_query.rb
new file mode 100644
index 00000000..65a62d1c
--- /dev/null
+++ b/lecture_4/homework/app/queries/mercenaries_query.rb
@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class MercenariesQuery
+  def self.available(relation: Mercenary)
+    relation.where(warrior_id: nil).where('available_from < ?', Time.now)
+  end
+
+  def self.cheapest(relation: Mercenary)
+    relation.order(price: :asc).first
+  end
+end
diff --git a/lecture_4/homework/app/services/warrior_recruiter.rb b/lecture_4/homework/app/services/warrior_recruiter.rb
new file mode 100644
index 00000000..1fb02149
--- /dev/null
+++ b/lecture_4/homework/app/services/warrior_recruiter.rb
@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+class WarriorRecruiter
+  attr_accessor :mercenary, :params
+  def initialize(mercenary:, params:)
+    @mercenary = mercenary
+    @params = params
+  end
+
+  def call
+    clan = find_clan
+    building = find_building
+    warrior_class = find_class(clan)
+
+    warrior = warrior_class.create!(
+      name: mercenary.name,
+      clan: clan,
+      building: building,
+      preferred_weapon_kind: mercenary.preferred_weapon_kind,
+      mercenary: @mercenary
+    )
+    create_good_weapon(@mercenary)
+    warrior
+  end
+
+  private
+
+  def find_class(clan)
+    clan.warriors.select('type, count(type) as warriors_count')
+        .group(:type).order('warriors_count ASC').first.class
+  end
+
+  def find_building
+    Building.find(@params[:building_id]) if @params[:building_id]
+  end
+
+  def find_clan
+    if @params[:clan_id]
+      Clan.find(@params[:clan_id])
+    else
+      Clan.order(warriors_count: :desc).first
+    end
+  end
+
+  def create_good_weapon(mercenary)
+    WeaponCreator.new(mercenary: mercenary).call
+  end
+end
diff --git a/lecture_4/homework/app/services/weapon_creator.rb b/lecture_4/homework/app/services/weapon_creator.rb
new file mode 100644
index 00000000..d8e346d6
--- /dev/null
+++ b/lecture_4/homework/app/services/weapon_creator.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+class WeaponCreator
+  attr_accessor :mercenary
+
+  def initialize(mercenary:)
+    @mercenary = mercenary
+  end
+
+  def call(mercenary)
+    case mercenary.preferred_weapon_kind
+    when :melee
+      Weapons::Katana.create!(warrior: mercenary.warrior, range: 2, damage: 25)
+    when :ranged
+      Weapons::Musket.create!(warrior: mercenary.warrior, range: 40, damage: 10)
+    else
+      Weapons::Rod.create!(warrior: mercenary.warrior, range: 42, damage: 10)
+    end
+  end
+end
diff --git a/recruitment_task/converter.rb b/recruitment_task/converter.rb
index 1a91dec6..a8e23fe1 100644
--- a/recruitment_task/converter.rb
+++ b/recruitment_task/converter.rb
@@ -1,5 +1,23 @@
 require_relative 'price'
 
-class Converter
-  # TODO: Implement me
+class Converter < Price
+  
+  EXCHANGE = {
+    eur: { pln: 4.32, eur: 1.00, usd: 1.13 },
+    usd: { pln: 3.81, eur: 0.88, usd: 1.00 },
+    pln: { pln: 1.00, eur: 0.23, usd: 0.26 }
+  }.freeze 
+  
+  def initialize(price)
+    @price = price
+  end
+
+  def convert_to(currency)
+    validate_currency(currency)
+    (@price.amount * EXCHANGE[@price.currency][currency]).round(2)
+  end
+
+  def validate_currency(currency)
+    raise InvalidCurrency unless SUPPORTED_CURRENCIES.include?(currency)
+  end
 end