The first thing that you need to know in order to do this problem

is the volume of a sphere of radius r.

The volume of a sphere of radius r is:

V(r) = (4/3) pi r^3.

So if the volume is 250 cm^3, we have:

250 =(4/3) pi r^3,

so:

r^3 = (3/4) 250/pi = 187.5 pi

hence:

r = cbrt(187.5 pi) ~= 8.382 cm

(cbrt denotes the cube root)

The rest are similar.

RonL