The radii of two spheres are 4ft and 8ft find the volume of a spheres whose surface area is equal to the sum of the surface areas of these two spheres.

Answer 1

V = (4/3)pi r^3

A = 4 pi r^2

4 pi r^2 = 4 pi (16) + 4 pi (64)

r^2 = 80 = 16*5

r= 4 * sqrt 5

so
(4/3) pi [ 4^3 *5 sqrt 5 ]