Answer:
14 minutes
Step-by-step explanation:
The barrel held 21 quarts of oil, which is equal to 84 cups. Trina drains the barrel at 6 cups per minute, so to find out how much time it takes her to drain it, divide 84 by 6:
84 / 6 = 14
So, it took Trina 14 minutes to drain the whole barrel.