40 coins. 25 and. 10 how many to make $7.75

D + Q = 40 so D = 40 - Q

.25Q +.10D = 7.75

substitute D = 40 - Q into. 25Q +.10D = 7.75

.25Q +.10D = 7.75

.25Q +.10 (40 - Q) = 7.75

.25Q + 4 -.10Q = 7.75

.15Q = 3.75

Q = 25

D = 40 - 25 = 15

answer

Quarter = 25 coins

Dime = 15 coins

double check

25 + 15 = 40 coins total

25 (.25) + 15 (.10) = 6.25 + 1.5 = 7.75

7.75

40 coins.

But you have a quarter and a dime. (.35)

so,

3 quarters, subtract. 35 = 75-35=40

There's my answer.