18. Five mark exercise problems VI

A man whose eye-level is \(2 \ m\) above the ground wishes to find the height of a tree. He places a mirror horizontally on the ground \(20 \ m\) from the tree and finds that if he stands at a point \(C\) which is \(4 \ m\) from the mirror \(B\), he can see the reflection of the top of the tree. How height is the tree?

 

The height of the tree \(=\)  \(m\)