X=quarters, y=dimes 7+2x=y 0.25x+0.1y=10.15 we substitute the first equation into the second equation 0.25x+0.1(7+2x)=10.15 0.25x+0.7+0.2x=10.15 0.45x+0.7-0.7=10.15-0.7 0.45x=9.45 0.45x/0.45=9.45/0.45 x=21 quarters 7+2x=y, x=21 7+2(21)=y 7+42=y y=49 dimes check: 0.25x+0.1y=10.15 when x=21, y=49 21(0.25)=5.25 in quarters 49(0.1)=4.90 in dimes 5.25+4.90=10.15