You must go to the water park for 8 days to make buying the season pass worth it.
<em><u>Explanation</u></em>
Suppose, the number of days you must go to the water park is 
Admission for the park is 17.50 per day. So, <u>the total cost for
days</u> will be: 
Given that, the season pass cost 125. So, the equation will be.....

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