The volueme of a rectangular prism is:
[tex]V=L\cdot W\cdot H[/tex]where L is the length, W is the wide and H is the hight
and in the figure we can see that one side of the prism has 12 blocks and a profundity of 3 so the correct expression will be:
[tex]\begin{gathered} 12+12+12 \\ or \\ 9+9+9+9 \end{gathered}[/tex]