Trying to learn the basics of C#

Question

Hi, I'm working on challenges to help me get used to c#. I know some c++, but I have a class next semester that is using c#, and I want a leg up.

 

The challenge is to find r2 given that (r1+r2) / 2 = s , or rather, the mean of two numbers. 

You're given r1 and s, so you use math or logic to find r2.

 

I can do this in two different ways. The first, is just algebra, and the other is a loop.

It's giving me a run-time error which can mean too much memory or compilation time too long.

 

Can anyone tell me why my code attempts are sketchy?

 

Thank you.