How to calulate how high a tree that is 5m high and shadow is 4m?

If you are trying to figure out the distance between the top of the tree and the end of the shadow, use a^2 + b^2 = c^2 where c is the hypotenuse and a and b are the legs of the right triangle.

5^2 + 4^2 = c^2

25 + 16 = c^2

41 = c^2

c = √41 = 6.4 meters