Pass a value to class from form and return value from class

Question

Hi. I am working on a window form and getting input from user through a Textbox . I want to involve those inputs to a class program and return to the form.

For example,

 I  get two inputs from a form  (A and B) .I want to involve those inputs to arithmetic operation  and get result and display it .The Arithmetic operations are done only by a class program. Can anyone suggest me How can i do that?