How do I require specific variables in the math input box

I am new to computational layer, but I can get the math input box to see y = 50x as correct, however I need the student to use different variables. The equation should be t = 50s based on the scenario given and I want the student to know which is the input variable and which is the output variable using the variables given in the scenario. How do I verify that they have used the proper variable names?

I only want the math input component not a graph component.

Here’s an example. It’s not necessarily the most efficient way but I tried to show what’s going on. It should be adaptable to whatever equation you need. Let me know if you have questions. equation with two variables • Activity Builder by Desmos Classroom

Thanks. That helped a lot.