Splashtown: 25 + 1x
Schlitterbahn: 40
25 + 1x = 40
-25 -25
0 1x = 15
x = 15
So after 15 rides, Schlitterbahn would be cheaper than Splashtown.
These tables have infinitely many values, but the simplest ones would be:
a) x|y
3|5
6|10
9|15
b) x|y
2|1
4|2
6|3
Your graph for c would look like the attached picture
ANSWER

EXPLANATION
The expressions are

and

The greatest common factor is the product the least powers of the common factors.

Wait isn’t it 30 or am I reading it wrong?