Question 23902
Let the dimes be d
Let the quarters be x


d = x-7
Dime value = 0.1 x 100 = 10
Quarter value = 0.25 x 100 = 25
total = 2.80 x 100 = 280


10d+25x=280
10(x-7)+25x=280
10x-70+25x=280
35x=350
x = 10


d = 10-7
d=3


Hence, there are 10 quarters and 3 dimes. 
Paul.