calculator with a 3 variable radio box

I'm new to javascript and I'm getting frustrated.

I have a formula that I want to use that has 3 variables.

x * y * a or b or c


a, b, and c are set values that I want to create a radio selection for and x and y need to be user entered via the form.

here's my lame attempt at a basic 3 entry script where the user puts in a, b, or c as an option...I'd prefer the radio box though....any help would be greatly appreciated:

 

nevermind got one to work....mods please delete this thread