Answer:
37.5% decrease
Step-by-step explanation:
Is there any more information than just that picture? Please tell me
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

8x-9y=11
First you move the 8x because you have to leave the 9y alone
8x-9y=11
-8x -8x
-9y=11-8x
Now you have to move the -9, so the inverse of multiplying is dividing so you divide -9.
-9y/-9= 11/-9 -8x/-9
since you can't have negative as a denominator it would be:
y= -11/9+8x/9
<span>You have to change the signs</span>
I don’t really understand what you mean could you be more specific please.