x=$5, y=$1
x+y=18
y=18-x
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.