Ratio of solidification time of a cube and sphere of same volume

Question

Volume of a cube of a side “l” and volume of sphere of radius ‘r’ are equal. Both the cube and the sphere are solid and same material. They are being cast. The ratio of the solidification time of the cube to the same of the sphere is

(a) $(4\pi /6)^{3}*(r/l)^{3}$                         (b)$(4\pi /6)*(r/l)^{2}$

(c)$(4\pi /6)^{2}*(r/l)^{3}$                          (d)$(4\pi /6)^{2}*(r/l)^{4}$