To find radius $ r $ use formula:

$$ V = \dfrac{ h ^{ 2 } \cdot r \cdot \pi}{ 3 } $$

After substituting $V = 235.5\, \text{cm}$ and $h = 9\, \text{cm}$ we have:

$$ 235.5\, \text{cm} = \dfrac{ 9\, \text{cm} ^{ 2 } \cdot r \cdot \pi}{ 3 } $$$$ 235.5\, \text{cm} \cdot 3 = 9\, \text{cm} ^{ 2 } \cdot r \cdot \pi $$$$ 706.5\, \text{cm} = 81\, \text{cm}^2 \cdot r \cdot \pi $$$$ r = \dfrac{ 706.5\, \text{cm} }{ 81\, \text{cm}^2 \, \pi} $$$$ r = 2.7764\, \text{cm}^-1 $$

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