Focus on the bottom left triangle. From this triangle, the bottom left corner has degree of 73. The base of this triangle is 20 feet.
We also can figure out the bottom right corner's degree. Since it forms a right angle with the 5 degrees next to it, the bottom right angle must be 85 degrees.
Which means the top corner of the triangle must be 180 - 73 - 85 = 22 degrees.
Now we can use law of sines to figure out the height of the tree:
height of tree = 20 feet
sin 73 sin 22
height of tree = 20 feet * sin73 = 51.1 feet
sin 22
