Please help me with this Physics question?

Question

A balloon is blown into a perfect sphere of outer diameter 10.0 inches. The density of the rubber is 1.25 g/cm^3. If the total mass of the rubber in the balloon is 24.0 g and the thickness of the rubber is uniform, what is that thickness?

Answer 1

Volume = Mass/Density = 24/1.25 = 19.2 cm^3

Formula for volume of a sphere with thickness = 4/3 * pi * [R^3 - r^3], where R represents outer radius and r inner radius.

19.2 = 4/3 * pi * [12.7^3 - r^3] (5 inches = 12.7 cm)

solve for 'r' then subtract from 'R' to get the thickness.