for a rectangular prism, the volume is,
the area of one of the faces * the length of the other unit
so say the base is 9 * 9, then, that base times the height of 16
now, for the triangular prism, the volume is,
the area of one of the triangular faces * the length of the other unit,
so... say, find the area of one of the triangular faces
recall 1/2 b*h
and then multiply that times the other length of 20
