An above-ground swimming pool in the shape of a cylinder has a diameter of 18 feet and a height of 4.5 feet. if the pool is filled with water to 6 inches from the top of the pool, what is the volume, to the nearest cubic foot, of the water in the pool? ⇆

The volume of a cylinder is

                                   (pi) (radius²) (height) .

Radius = 1/2 diameter.
Radius of this pool = (1/2) (18 ft) = 9 ft

The pool is a cylinder with height of 4.5 feet. 
The water in it is also a cylinder, but only 4 ft high.

Volume of the water =

             (pi) x (radius²) x (height)

         =  (pi)  x  (9 ft)²  x  (4 ft)

         =  (pi)  x  (81 ft²)  x  (4 ft)

         =  (pi)  x  (324 ft³)  =  1,017.9 ft³ .