Question 1151475
N+D=30 count equation
.05N+.10D=2.10 money equation
N=30-D  substitute
.05(30-D)+.10(D)=2.10
1.5-.05D+.10D=2.10
0.5D=0.60
D=12
N=18
$1.20+$0.90=$2.10