Let the number of nickels = N
The number of quarters =N + 7
0.05N + 0.25[N + 7] = 3.55
0.05N + 0.25N + 1.75 = 3.55
0.3N = 3.55 - 1.75
0.3N = 1.8
N = 1.8 / 0.3
N = 6 - number of nickels
6 + 7 = 13 - Number of quarters
Check: [6 x 0.05] + [ 13 x 0.25] =0.30 + 3.25 =$3.55
