$\mathit{H}\mathit{o}\mathit{w}\mathbf{ }\mathit{d}\mathit{i}\mathit{d}\mathbf{ }\mathbf{4}\mathbf{ }\mathit{c}\mathit{o}\mathit{t}\mathbf{ }\mathit{\theta }\mathbf{ }\mathbf{\times }\mathbf{ }\mathbf{9}\mathbf{ }\mathit{t}\mathit{a}\mathit{n}\mathbf{ }\mathit{\theta }\mathbf{ }\mathit{b}\mathit{e}\mathit{c}\mathit{o}\mathit{m}\mathit{e}\mathbf{ }\mathbf{36}\frac{\mathbf{1}}{\mathbf{t}\mathbf{a}\mathbf{n}\mathbf{ }\mathbf{\theta }}\mathbf{ }\mathbf{\times }\mathbf{ }\mathit{t}\mathit{a}\mathit{n}\mathbf{ }\mathit{\theta }\mathbf{ }\mathbf{:}$
$$\begin{gathered} \Rightarrow \frac{h}{4}= cot \theta \\ \Rightarrow h=4 cot \theta \\ In △ABQ, \frac{AB}{QB}=\tan \theta \\ \frac{h}{9}= \tan \theta \\ h=9 \tan \theta \\ From equation \left(i\right) and \left(ii\right), we get \\ h\times h=4 cot \theta \times 9 \tan \theta \\ \Rightarrow h^2=36 cot \theta \times \tan \theta =36\frac{1}{\tan \theta }\times \tan \theta \\ \Rightarrow h^2=36 \Rightarrow h=6 m. \end{gathered}$$