Working together, edith and rupert can pick 3 quarts of blueberries in an hours. how many quarts can they pick in 7 hours?

Since they pick 3 quarts in 1 hour they can pick 6 quarts in 2 hours and 9 quarts in 3 and so on. So the number of quarts they can pick in a certain amount of hours is just the total number of hours they spend picking times 3 quarts. So since they picked for 7 hours and each of those hours they picked 3 quarts, in total they picked 21 quarts

7 x 3 = 21 quarts