Explanation:
what's the problem ? your teacher even gave you the formula for the volume of a sphere and allowed you to round pi to simply 3. and he gave you the radius directly (not even "hidden" as diameter).
so, what is it you cannot do by yourself ? if you are unsure about doing these calculations in your head, use a calculator.
this is all much, much faster than uploading such a question here and waiting for a response, which very often will just be nonsense, because some people here just only make fun of such simple questions.
r = 7
pi = 3
so,
V = 4/3 × 3 × 7³ = 4 × 7³ = 4 × 343 = 1372 cm³
that's it.
please, when you have the time let me know, where the problem was, and if I can help you better understanding this problem.