Solution:

Given internal diameter of hollow sphere = 4 cm

Internal radius, r = 4/2 = 2 cm

External diameter = 8 cm

External radius, R = 8/2 = 4 cm

Volume of the hollow sphere, V = (4/3)(R³-r³)

V = (4/3)×(4³-2³)

V = (4/3)×(64-8)

V = (4/3)×56

Base diameter of the cone = 8 cm

Radius, r = 8/2 = 4 cm

Volume of cone = (1/3)r²h

= (1/3)×4² ×h

= (16/3)×h

Since sphere is melted and changed into a cone, their volumes remain same.

(4/3)×56 = (16/3)×h

h = 4×56/16

h = 14 cm

Hence the height of the cone is 14 cm.