How many gallons are in a 4 foot by 12 foot by 18 foot round swimming pool?
The dimensions stated above in the reworded question are for an oval pool, not a round one. I suspect the original question was for a round pool with an 18′ diameter and a 4.5′ wall. (The slash in 4 1/2 did not show up in the question.) If that is the case, then the is 3.14 times 81 times 4.5 divided by 7.5.