A circular pool is 3.5 meters deep and has a radius of 9 meters what is the volume?

The volume of a cylinder is the area of its base multiplied by the height. [In this case, the "height" of the cylinder is the depth of the pool.]

The base of the pool is a circle with radius of 9 m. The area of a circle is the radius squared times pi, which in this case is 81*pi m^2. Multiply this by the depth of 3.5 and you get 283.5 * pi cubic meters.