check the picture below.
so it has a base of 18x18 and a height of that much.
[tex] \bf \textit{volume of a pyramid}\\\\
V=\cfrac{1}{3}Bh~~
\begin{cases}
B=area~of\\
\qquad its~base\\
h=height\\
------\\
B=\stackrel{18\times 18}{324}\\
h=12
\end{cases}\implies V=\cfrac{1}{3}(324)(12)\implies V=1296 [/tex]
