To find volume $ V $ use formula:
$$ V = \dfrac{ \sqrt{ 3 } \cdot a ^{ 2 } \cdot l }{ 2 } $$After substituting $ a = 3.4 $ and $ l = 3.5 $ we have:
$$ V =\dfrac{ \sqrt{ 3 } \cdot 3.4 ^{ 2 } \cdot 3.5 }{ 2 } $$$$ V = \dfrac{ 20.0225 \cdot 3.5 }{ 2 }$$$$ V = \dfrac{ 70.0788 }{ 2 } $$$$ V = 35.0394 $$