so, the prism looks more or less like the picture below
now, notice the purple base, is a triangle with all sides of 9
[tex]\bf \textit{area of an equalateral triangle}\\\\
A=\cfrac{s^2\sqrt{3}}{4}\qquad
\begin{cases}
s=\textit{length of one side}\\
----------\\
s=9
\end{cases}\implies A=\cfrac{9^2\sqrt{3}}{4} \\\\
-----------------------------\\\\
\textit{volume of a pyramid}\\\\
V=\cfrac{1}{3}Bh\qquad
\begin{cases}
B=\textit{area of the base}\\
h=height\\
----------\\
B=\frac{81\sqrt{3}}{4}\\
h=8
\end{cases}\implies V=\cfrac{1}{3}\cdot \cfrac{81\sqrt{3}}{4}\cdot 8[/tex]
