You can put this solution on YOUR website! Pyramids and cones are quite similar in terms of shape (one could claim that they are "topologically equivalent" -- that is, one could continuously transform the pyramid to obtain the cone, vice versa).
Therefore, their volume formulas are the same. The volume V of a pyramid or cone is equal to
where A is the area of the base and h is the height. This formula is derived using integral calculus; you assume that the pyramid or cone is composed of arbitrarily thin "sheets" stacked on each other, compute the volume of each "sheet" with the height being some infinitely small number (denoted dh), then adding those up via an integral.