How to calculate math operations in textBox? : <p><a href="https://i.stack.imgur.com/beWnP.jpg" rel="nofollow noreferrer">App image</a></p>

<p>Hi guys, I'm a beginner in programming and I'm trying to make a math game. I don't know how to make a program calculate whats inside of the textbox. When player clicks a button with number or operator, app writes that in a textBox under the buttons. After clicking 'OK' app should compare number on the top(303) with players calculation. Any ideas how to make this work?</p>
