Answer
S=4$\pi$R$^2$+4$\pi$r$^2$
Work Step by Step
The desired surface area is the sum of the outer and inner surface areas. The formula for the surface area of the outer sphere with radius of a length R, would be:
S=4$\pi$R$^2$
The formula for the surface area of the inner sphere with radius of length r, would be:
S=4$\pi$r$^2$
Add these two values to get the formula for the total surface area of the hollow-core sphere:
S=4$\pi$R$^2$+4$\pi$r$^2$
