We'll use the formula to compute the volume of a pyramid:
[tex]V=\frac{1}{3}Bh[/tex]Where B is the area of the base and h is its height. We begin by computing the area of the base:
[tex]B=5\cdot3=15[/tex]And now we can compute the area of the pyramid
[tex]V=\frac{1}{3}15\cdot4=20[/tex]Thus
[tex]V=20in^3[/tex]