To find volume $ V $ use formula:
$$ V = \dfrac{ 4 \cdot r^2 \cdot \pi}{ 3 } $$After substituting $ r = 3 $ we have:
$$ V = \dfrac{ 4 \cdot 3^2 \cdot \pi}{ 3 } $$ $$ V = \dfrac{ 4 \cdot 9 \cdot \pi}{ 3 }$$ $$ V = \dfrac{ 36 \cdot \pi}{ 3 }$$ $$ V = 12 \cdot \pi $$