x - the number of five dollar bills
y - the number of one dollar bills
She has 18 bills in total.
\(x+y=18 \\ y=18-x\)
She has $62.
\(5x+y=62 \\
y=62-5x\)
Set both expressions equal to each other:
\(18-x=62-5x \\
-x+5x=62-18 \\
4x=44 \\
x=11 \\ \\ y=18-x=18-11=7\)
She has 11 five dollar bills and 7 one dollar bills.
