If all you want to do is evaluate mathematical operations, then executing VB code is overkill. Have a look at this:
Math Parser .NET C#
] You feed ita string, it returns the result.
While you can compile and execute VB code from within a program, it is a lot more complex to do, and a lot more dangerous (since it will have access to all the .NET methods, which is probably not what you want at all!)