radius = 3 feet
rearrange the formula making r the subject
[tex]\frac{4}{3}[/tex] πr³ = V ( multiply both sides by 3 to eliminate fraction )
4πr³ = 3V ( divide both sides by 4π )
r³ = [tex]\frac{3V}{4\pi }[/tex] = ( 3 × 36π ) / 4π = 3 × 9 = 27
take the cube root of both sides
r = [tex]\sqrt[3]{27}[/tex] = 3
