You must go to the water park for 8 days to make buying the season pass worth it.
Step-by-step explanation
Suppose, the number of days you must go to the water park is

Admission for the park is 17.50 per day. So, the total cost for
days will be:

Given that, the season pass cost 125. So, the equation will be.....

(As the number of days can't be in decimal)
So, you must go to the water park for 8 days to make buying the season pass worth it.