8+d=the number of quarters

d=the number of times

total money=6.20

each quarter is worth .25 each dime worth .10

.25 (8 + d) + .10(d)= 6.20

2.00 + .25d + .10d= 6.20 (subtract to get variables alone)

.35d=4.20 (divide by .35 to solve for d)

d=12

There are 12 dimes or $1.20 worth. There are 12 + 8=20 quarters or $5 worth of quarters.