Answer:
Input variable x: Number of classes he attends.
Output variable y: Monthly cost
Slope: Cost per class, of $2
y-intercept: Membership fee, of $25.
Function: 
Step-by-step explanation:
This situation can be represented by a function is the following format:

In which y is the monthly cost(output), m is the cost per class(slope), x is the number of classes he attends(input) and b is the membership fee(y-intercept).
We have that:
There is a membership fee of $25 per month and a fee of $2 per workout class he attends.
This means that
. So
