In this problem situation you have three factors that give you the "guidelines" of your equation you must find in order to find the amount of the amount of rides you can go on.
Since you have to pay $13 in order it enter the amusement park, you would automatically subtract $13 from your set budget. This leaves us $22.50 as your budget.
1) 35.5-13=22.5
Now you simply divide your budget by $1.50 because you want to see how many rights you can fit in your budget.
2) 22.5/1.5=15
You can ride 15 rides with a budget of $35.50
3) 15 rides