a) Let, number of release movies = x
Then, for members of a club it is: = 15 + 2x
For non-members it is: 3x
b) It would be beneficial to have a membership when:
15 + 2x = 3x
15 = 3x-2x
x = 15
It means, It would be beneficial to have a membership when you need to release more than 15 new releases
Hope this helps!