That is incorrect seeing as you posted the calculation for the pool being (length * width * depth) not (length + width) * depth.

First we convert our yards to feet. The first would be (50 x 3) = 150. The second (20 x 3) = 60.

Now we use our formula and multiply all the feet.

150 * 60 * 9 = 81000 cubic feet.

Now seeing as 1 cubic foot holds the 7.5 gallons we multiply the (81000 * 7.5) and get 607500 gallons.

First we convert our yards to feet. The first would be (50 x 3) = 150. The second (20 x 3) = 60.

Now we use our formula and multiply all the feet.

150 * 60 * 9 = 81000 cubic feet.

Now seeing as 1 cubic foot holds the 7.5 gallons we multiply the (81000 * 7.5) and get 607500 gallons.