Correct. Find the volume of the cube and subtract the volume of the pyramid from it.

Volume of cube: $\displaystyle{{a}}^{{3}}\usepackage{cmbright}\Huge\$ $\displaystyle=\usepackage{cmbright}\Huge\$ $\displaystyle{{6}}^{{3}}={216}\usepackage{cmbright}\Huge\$

Volume of pyramid: $\displaystyle\frac{{1}}{{3}}{l}{w}{h}=\frac{{1}}{{3}}{\left({6}\right)}{\left({6}\right)}{\left({6}\right)}=\frac{{1}}{{3}}{\left({216}\right)}={72}\usepackage{cmbright}\Huge\$

Volume of solid: $\displaystyle{216}-{72}={144}\usepackage{cmbright}\Huge\$ cubic meters