assuming is a 9 inch side.
[tex]\bf \textit{area of an equilateral triangle}\\\\
A=\cfrac{s^2\sqrt{3}}{4}\qquad
\begin{cases}
s=length~of\\
\qquad a~side\\
-------\\
s=9
\end{cases}\implies A=\cfrac{9^2\sqrt{3}}{4}\implies A=\cfrac{81\sqrt{3}}{4}[/tex]
