You can draw a right triangle with theses measures:
elevation angle = 42°
base = adjacent angle = distance from the base of the three to where the man is standing.
height = opposed angle ≈ height of the tree = 20 feet.
Note: this is assuming that the elevation angle is from the ground (this is the man is looking laying on the ground).
=> tan(42) = opposed angle / adjacent side => 20 feet / x
=> x = 20 feet / tan(42) = 22.21 m
Answer: option C. 22,2 feet
