Alex usually runs for 21 hours a week,
training for a marathon. if he is unable
to run for 3 days, describe how to find
out how many hours of training time he
loses, and write the appropriate integer to
describe how it affects his time. plz

Alex runs 21 hours a week.
Since, a week has 7 days, he runs, 21 hours in 7 days.
Now,
In 7 days, Alex runs 21 hours
In 1 day, Alex runs 21 / 7 hours
                            = 3 hours
In 3 days, Alex runs 3 * 3 hours
                           = 9 hours.
 
So, If he is unable to run for 3 days, he loses 9 hours of his training time.