Find the volume of a solid

My approach is to divide the solid into two. One is a cuboid and the other is a frustum of a regular pyramid. The volume of the cuboid is $8 \times 8 \times 2 = 128~m^3$ .

The formula for the volume of a frustum of a regular pyramid is given by $v=\dfrac{h}{3}(A_1+A_2+\sqrt{A_1 \times A_2})$ where $A_1$ and $A_2$ are the area of the bases of the frustum of the regular pyramid. So the volume of the frustum of the regular pyramid is

$v=\dfrac{4}{3}(8^2+2^2+\sqrt{8^2+2^2}=112)$

The desired volume is 128+112 = 240~\text{m^3}