# marcy has a total of 100 dimes and quarters. if the total value of the coins is $14.05, how many quarters does she have?

You need two equations to substitute into each other. You need one for the total number of coins, and one for the amount.

d=# of dimes

q=# of quarters

d+q=100

.10d+.25q=14.05

Get how I got those equations? See if you can solve the rest. If you can't, post again, and I'll see if I can help you.