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
