Answer: 21 quarts
Explanation:
Given : Working together,Edith and Rupert can pick 3 quarts of blueberries in an hour.
i.e. The number of quarts of blueberries they pick in one hour = 3
Then, the number of quarts they can pick in 7 hours is given by :-

Hence, the number of quarts they can pick in 7 hours is 21 quarts.