[tex]\bf \textit{total surface area of a cone}\\\\
s=\pi r\sqrt{r^2+h^2}+\pi r^2\quad
\begin{cases}
r=radius\\
h=height\\
-----\\
r=12\\
h=9
\end{cases}
\\\\\\
s=\pi (12)\sqrt{12^2+9^2}+\pi (12^2)\implies s=12\pi \sqrt{225}+144\pi
\\\\\\
s=12\pi (15)+144\pi \implies s=180\pi +144\pi \implies s=324\pi [/tex]
