Plug in the dimensions to the formula given using a handy dandy calculator for both problems.
1. The diameter of the bottom of the cone is 4 so the radius (half that) is 2. Volume = 1/3 * pi * (2)² * 6
= 1/3 * pi * 4 * 6
= 1/3 * pi * 24
= 8 * pi
≈ 25.1327 cm³
2. They give you all you need, the radius.
Volume = 4/3 * pi * (6)³
= 4/3 * pi * 216
= 288 * pi
≈ 904.7787 in³
