
Bradford T. answered 05/20/21
Retired Engineer / Upper level math instructor
If you draw a picture of the building and tower
+--------------------------------
|\ 35.9° = θ
| \
30| θ \
+----+
| x |
20| | Building
+----+
x
From the picture and opposite angles of parallel lines are equal
tan(39.5°) = 30/x
x = 30/tan(39.5°) ≈ 36 feet