Answer:
You have 12 quarters and 30 dimes.
Explanation:
If you have an equation that says 10d+25q= 600 cents (d meaning dime and q meaning quarter) and have another equation that says d+w=42, then you could use those two equations to solve the problem.
Hope this helps a little bit. It is a little hard to explain but let me know if you need some more help.