answer: 21 minutes
work: okay, so to solve this we need to find the unit rate, or number of minutes he spends doing pushups each day, to be ale to see how many he does in 7 days.
so, to find the unit rate, divide the number of minutes by days.
9/3 = 3
so, this means he spends 3 minutes a day on pushups.
to find out how many he completes in 7 days, multiply how many minutes he spends a day (3) by the number of days (7)
3 x 7 = 21
so, he spends 21 minutes doing pushups in 7 days.