5x+y=62 (take the equation y=18-x and plug into y) 5x+(18-x)=62 (combine like terms) 5x-x+18=62(subt. 5x and x) 4x+18=62 (subt. 18 from both sides) 4x=62-18 4x=44(now divide by 4) x=44/4 x=11(now take 11 and plug into the equation x+y=18, 11+y=18=y=18-11, y=7 so it would be 11=$5 bills and 7-$1 bills.