To find height $ h $ use formula:
$$ V = \dfrac{ a ^{ 2 } \cdot h }{ 3 } $$After substituting $ V = 196 $ and $ a = 7 $ we have:
$$ 196 = \dfrac{ 7 ^{ 2 } \cdot h }{ 3 } $$$$ 196 \cdot 3 = 7 ^{ 2 } \cdot h $$$$ 588 = 49 \cdot h $$$$ h = \dfrac{ 588 }{ 49 } $$$$ h = 12 $$