To find radius $ r $ use formula:
$$ V = \dfrac{ 4 \cdot r^2 \cdot \pi }{ 3 }$$After substituting $ V = 271.8 $ we have:
$$ 271.8 = \dfrac{ 4 \cdot r^2 \cdot \pi }{ 3 }$$ $$ 271.8 \cdot 3 = 4 \cdot r^2 \cdot \pi $$ $$ 815.4 = 4 \cdot r^2 \cdot \pi $$ $$ r^2 \cdot \pi = \dfrac{ 815.4 }{ 4 } $$ $$ r^2 \cdot \pi = 203.85 $$ $$ r = \sqrt{ \frac{ 203.85 }{\pi} } $$ $$ r \approx 8.0553 $$