Question 11373
Set the formula for the volume of the sphere = twice the formula for the surface area of the sphere and solve for r..

{{{(4/3)(pi)r^3 = 2(4(pi)r^2)}}}  solve for r. Divide both sides by {{{(pi)r^2}}}

{{{(4/3)r = 8}}}  Multiply both sides by (3/4)

{{{r = 6}}}