john has$1.70 . he has 3 more dimes than quarter.

Calculus? You are dreaming.

.1D+.25Q=1.70
d-3=Q
d=Q+3
.1(Q+3)+.25Q=1.70
.35Q=1.70-.3
Q= 1.40/.35 = 4 D= 7

Your teacher is too easy.