Bobbie has 45 coins in dimes and quarters. The total value of the coins is $7.65. How many quarters and dimes does have?

q + d = 45

q = 45-d

10d + 25q = 7.65

Substitute 45-d for q in last equation and solve for d. Insert that value into the first equation and solve for q. Check by inserting both values into the last equation.