Answer
The tower's height is $21m$.
Work Step by Step
In a simple pendulum, $$\frac{2\pi}{T}=\sqrt{\frac{g}{L}}$$ $$\frac{g}{L}=\frac{4\pi^2}{T^2}$$ $$L=\frac{gT^2}{4\pi^2}$$
The pendulum's period $T=9.2s$. The tower's height, therefore, is $$L=21m$$
