Answer:
25 : 64
Step-by-step explanation:
To get the ratio of the surface area of the smaller sphere to that of the larger sphere, we must understand first what the surface area of  a sphere is. A sphere with radius r has a surface area A given as
A = 4πr²
As such, if the smaller sphere has a radius r and the larger a radius R then the ratio of the surface areas of the two spheres
= 4πr² : 4πR²
= r² : R²
If r : R is 5:8 then the ratio of the surface areas
= 5² : 8²
= 25 : 64
