If you wanna know which one's better, you've gotta formulate them both. Let's say x is the number of movies you rented.
A: 37.92+2.18x
B: 33.25+3.55(x-1)
A B
- 40.10 33.25
- 42.28 36.80
Keep going on to see that B is better in the short term, but A is better long term.