Chelsea already spent $20 and $15:

So now she has $10 left to spend on the game she wants to play. If the number of times she plays this game is x and the game costs $0.65, you can model this with the following inequation:

If we clear the x from here, we can find the maximum number of times that Chelsea can play this game:


Since the number of times she can play must be a whole number (you can't play 15.3 times) and this number must be under 15.3846, the maximum number of times Chealsea can play this game is 15.
Bonus: if you substract 15 from the previous result and multiply by how much the game costs, you can get how much money Chealsea has left:

So she leaves the fair with $0.25 after playing the maximum number of times on the game.