Total Area = 8000 ft^2
Stock Area = 4000 ft^2
h = 20 ft
Stock's Volume = 4000*20 = 80000 ft^3
Boxes's Volume = 15*7*6 = 630 ft^3
Now he need to find how many boxes can stock in the warehouse space
80000/630 = 127 boxes. And if each box has two cans:
127 * 2 = 254 cans can be stored.