How to display the current version present on the system, in the version Downgrade Message for Bootstrapper Application

[sansa20]

I have created a bootstrapper project which uses an msi being generated in my wixsetup project.
In my Wixsetup project's wxi file I have set my error message using the MajorUpgrade element. However is there anyway I can display the application version already present on the system.
For example, my system has version 3.8 already installed and I try to install version 2.2. So the error message I would like to display is "Can't downgrade to an older version as version 3.8 is present on this system". Is this possible because I am unable to find out where in the code the current version on system is being read. I would really appreciate some help on this.