By drawing a diagram that represents the problem, obtain triangle ABC such that
m∠A = 45°
AB = 15 ft, distance downhill
Let BC = h, the vertical height of the tree.
Because AB is 20° above the horizontal, m∠C = 90 -(20+45) = 25°.
Apply the Law of Sines to obtain
[tex] \frac{h}{sin45} = \frac{15}{sin25} [/tex]
[tex] h=15(\frac{sin45}{sin25} )=25.1[/tex]
Answer: 25 ft (nearest foot)