## Algebra 2 (1st Edition)

$\frac{720}{7}\approx102.86$ minutes
In one hour we can wash $\frac{60}{15}+\frac{60}{20}=4+3=7$ windows together. Hence we will need $\frac{12}{7}$ hours to wash twelve windows, which is $\frac{720}{7}\approx102.86$ minutes