The surface area of a sphere is S=4πr2S = 4\pi r^2S=4πr2. Solve for rrr in terms of SSS.
r=S4πr = \sqrt{\frac{S}{4\pi}}r=4πS
r=S4πr = \frac{S}{4\pi}r=4πS
r=S4πr = \frac{\sqrt{S}}{4\pi}r=4πS
r=4πSr = \sqrt{\frac{4\pi}{S}}r=S4π