Since V = (4/3) pi*r^3, r^3 = V / [(4/3)*pi ].
1200 ft^3
Here, r^3 = ---------------
[(4/3)*pi ]
Evaluate this, and then take the cube root of your result, and then you'll have the radius.
Once you have this radius, the surface area will be A = 4*pi*r^2.
