l: The length of the base of the prism

w: The width of the base of the prism

h: The height of the prism

V: The volume of the interior of the prism

In general, the volume of a pyramid is one-third the volume of a corresponding prism (with a base congruent to that of the pyramid and a height equal in measure to that of the pyramid).

As a result, the volume of a pyramid is one-third the area of the base times the height of the pyramid.

The area of the rectangular base is given by the formula A = lw

Substitute to get the following:

Simplify to get the final result: