Because the angle of light hitting the ground is the same, the angle between light and the tree is 30 degrees, and the angle between light and the parallel line on the ground is 60 degrees. ∠CFD and∠ ∠AHE are similar angles. Trees must be perpendicular to the ground, so AE is perpendicular to HG.

The right-angled side corresponding to 30 degrees is half of the hypotenuse. That is, BE= 1/2BH=6cm.

His square = the square of BH-the square of BE = 108?

Because? AH=2HE？ So AH square =4 times HE square -4X 108.

Because AH party -HE party =AE party?

So AE squared =4X 108- 108=324.

So AE= 18.

So AB = AE-BE =18-6 =12cm.