what is the distance between two buildings, the shorter one is 200 meters with a depression of 20degrees and the longer one's height is unknown with an elevation of 10degrees

Answer 1

Please use the proper mathematical terms. We use "angle of depression" and "angle of elevation".
"Depression" is for psychologists.

We also need the position/location of the observer. Is the observer at a point between the buildings, or is the observer on the same side of both buildings, or is the observer at the same distance from both buildings?