ANSWER
307½ gallons of water
Step-by-step explanation
The volume of the rectangular swimming pool is

where l=25ft and w=20½ ft.
when it is filled to a depth of 4½ ft ,then the height is , h=4½ ft.
We substitute these values into the formula to get:


If one cubic foot of water is 7½ gallons, then 2306.25 cubic feet will be

We need 307.5 gallons of water to fill the pool.