how do i simplify the equation 31=2pi/3 *r
\(31=\frac{2\pi}{3}r\\ 31=\frac{2\pi}{3}r\\ 31=r\times\frac{2\pi}{3}\\ \text{You need of get rid of the }\frac{2\pi}{3}\quad so \\ \text{Multiply BOTH sides by the reciprocal, that is }\times\frac{3}{2\pi} \)
You can finish it :)