If Jason have 90 pills and have to take 3 pills a day for 3 weeks how many pills do Jason have left?

If Jason have 90 pills and have to take 3 pills a day for 3 weeks how many pills do Jason have left?

1 week = 7 days
3 weeks = 7 days * 3 = 21 days
3 pills per day * 21 days = 63 pills

Subtract the 63 pills from the 90 pills to get:
90 - 63 = 27 pills left