How do I solve this mathematical word problem without using trial and error?

Timmy has almost $2.00 in allowance money that he wants to spend on candy. He has two favorite candies, one selling at $0.15 a piece and one at $0.08 a piece. If he ends up spending $1.92 on 17 pieces of candy, how many $0.15 pieces of candy did Timmy decide to buy?

Is there a formula I can apply to this? Find the answer and show me how you did it.