Question 342409
no. of dimes=x
no. of quarters = y

from 1st condition,
x*.10+y*.25=30.50

from 2nd condition,
x-4=y

substitution value of y in 1st equation,

x*10+(x-4)*25=30.50
solving we get 
no. of dimes :90
no.of quater: 86