Alright, to do this problem you need the formula for the volume of a sphere:
V= [tex] \frac{4}{3} [/tex][tex] \pi [/tex][tex]r^3[/tex]
Then plug in the radius and solve!
V= [tex] \frac{4}{3} [/tex][tex] \pi [/tex][tex]2.1^3[/tex]
V= 38.8 cm
The answer is the same if you needed to use 3.14
I hope this helped!