[tex]\bf \textit{circumference of a circle}\\\\
C=2\pi r~
\begin{cases}
r=radius\\
-----\\
C=16\pi
\end{cases}\implies 16\pi =2\pi r\implies \cfrac{16\pi }{2\pi }=r\implies \boxed{8=r}\\\\
-------------------------------\\\\
\textit{area of a circle}\\\\
A=\pi r^2\qquad \qquad \qquad \implies A=\pi (8)^2\implies A=64\pi [/tex]
