#### Answer

$$105840 \mathrm{J}$$

#### Work Step by Step

The volume of one layer is 4 $\Delta y \mathrm{m}^{3}$ and so the weight of one layer is $23520 \Delta y$ N. Thus, the work done against gravity to build the tower is
\begin{align*}
W&=\int_{0}^{3} 23520 y d y\\
&=\left.11760 y^{2}\right|_{0} ^{3}\\
&=105840 \mathrm{J}
\end{align*}