The circumference of a circle of radius r is given by:
[tex]C=2\pi r[/tex]
For this question we simply need to take C=36π and solve for r:
[tex]36\pi=2\pi r[/tex]
If we divide both sides by 2π we get:
[tex]\begin{gathered} 36\pi=2\pi r \\ \frac{36\pi}{2\pi}=\frac{2\pi r}{2\pi}=\frac{2\pi}{2\pi}\cdot r \\ 18=r \end{gathered}[/tex]
Then the answer is option A, 18.
