Also, let the distance between the tower $(BD)$ and the cliff $(AC)$ be $d\mathrm{m}$.
Thus, in △ABC, tan x = $\displaystyle \dfrac{{20}}{d}$ ​……(i)
Also, in △CDE, tan x = $\displaystyle \dfrac{h}{d}$
​………(ii)
From equations (i) and (ii)
$\displaystyle \dfrac{h}{d}$ ​= $\displaystyle \dfrac{{20}}{d}$​
$\Rightarrow h=20\mathrm{m}$
$\Rightarrow$ Height of the tower is $20+20=40\mathrm{m}$.