[tex]\bf \textit{area of a circle}\\\\
A=\pi r^2\quad
\begin{cases}
r=radius\\
-----\\
A=25\pi
\end{cases}\implies 25\pi =\pi r^2\implies \cfrac{25\pi }{\pi }=r^2
\\\\\\
25=r^2\implies \sqrt{25}=r\implies 5=\boxed{r}\\\\
-------------------------------\\\\
\textit{circumference of a circle}\\\\
C=2\pi r\qquad \qquad C=2\pi\left( \boxed{5} \right)\implies C=10\pi [/tex]
