Answer
1296 $in.^{3}$
Work Step by Step
Volume = $\frac{base area \times h}{3}$
Base area = $(18 in.)^{2}$ = 324 $in.^{2}$
h = $\sqrt ( (slant height)^{2} - (\frac{side of the base}{2})^{2})$
h = $\sqrt ( (15 in.)^{2} - (\frac{18 in.}{2})^{2})$
h= 12 in.
Volume = $\frac{324 in.^{2} \times 12 in.}{3}$
Volume = 1296 $in.^{3}$
