Question 371197
q+d=30 ----> q=30-d
25q+10d=405
25(30-d)+10d=405
750-25d+10d=405
750-15d=405
-15d=405-750
-15d=-345
d=-345/(-15)
d=23
q=30-d=30-23=7

Answers: 23 dimes, 7 quarters