Answer:
8 minutes
Explanation:
We know that in 4 minutes, 16 gallons of water are added. We also know that we need to get 32 gallons of water in total.
If 16 x 2 =32, we know that we can add 16 more gallons of water to get 32 in total. This makes the problem easier to solve, because we are already told how many minutes it takes for 16 gallons to be added. If it takes 4 minutes for each 16 gallons, we just do 4 x 2 = 8.