feat: adds completed calculator function

Author: mercedes-mathews

lesson_06/expression/.env.test

@@ -1 +1 @@
-HW_VERSION=your assigned version here
+HW_VERSION=D

lesson_06/expression/src/expression_calculator.ts

@@ -2,10 +2,22 @@ export class ExpressionCalculator {
   /** Returns a calculation involving a, b, c, d, and e */
   calculate(a: number, b: number, c: number, d: number, e: number): number {
     // Implement your code here to return the correct value.
-    return 0;
+    return this.divide(this.multiply(a, b), this.pow(this.add(c, d), e));
   }
 
   pow(base: number, exponent: number): number {
     return Math.pow(base, exponent);
   }
+
+  add(a: number, b: number): number {
+    return a + b;
+  }
+
+  multiply(a: number, b: number): number {
+    return a * b;
+  }
+
+  divide(a: number, b: number): number {
+    return a / b;
+  }
 }