To find height $ h $ use formula:
$$ V = h ^{ 2 } \cdot r \cdot \pi$$After substituting $V = 678.6\, \text{cm}$ and $r = 4\, \text{cm}$ we have:
$$ 678.6\, \text{cm} = 4\, \text{cm} \cdot h ^{ 2 } \cdot \pi $$$$ h ^{ 2 } = \dfrac{ 678.6\, \text{cm}}{ 4\, \text{cm} \, \pi } $$$$ h ^{ 2 } \approx 54.0011 $$$$ h \approx \sqrt{ 54.0011 } $$$$ h \approx 7.3485 $$