Given that the generatrix of a cone is 5cm in length and 4cm in height, how to find the volume of the cone?

Given that the generatrix of a cone is 5cm in length and 4cm in height, how to find the volume of the cone?

If the generatrix is 5cm long and 4cm high, the radius of the bottom is 3cm (Pythagorean theorem)
So the bottom area is 9 π
The volume is 1 / 3 * 9 π * 4 = 12 π