Practice Problem: Simple Math Problem

A Programing Practice Problem where the user is a studying math student.

Math Problem

Create a Form with the math problem of x + y = z
x and y should be displayed via label, z as a textbox.
There should be a submit button, which will store wether or not the user was right, and give the user a new problem. z's textbox should be cleared upon submit.
After ten questions, display the test results to the user in a method of your choosing (ex. results label, messagebox, output to file)

Once you have completed the above, consider extras from below:
-The user can select other math symbols (-, /, *) as part of the test
-Provide the user with a final grade
-Use a time limit per question/test
-Track the problems and answers as part of the end of test output
-Show multiple problems at the same time (and still track all of them as one test)

How difficult was it to make changes to the program after its initial creation?
What could have been done differently in the initial creation to allow changes to be made easier?
Did you use any other classes other than the original form?
What objects could have been created to take better advantage of Object Oriented Programming?