Trying to find equation- please help

Lisa has a collection of nickels, dimes, and quarters worth 15.75. She has 10 more dimes than nickels and twice as many quarters as dimes. How many coins of each kind does she have?

I have tried this problem over and over and I can't figure out what formula to use. If someone can help me w/ finding the formula I can solve it.

You have \(\displaystyle .05N+.10D+.25Q=15.75, D=N+10,Q=2D\).