Answer:
I guess we want to find the distance between the bottom of the tree and the swingset.
The data we have is:
Emir is 11 m above the ground.
The angle of depression (this is, the angle from the horizontal line that goes through Emir point of view to the actual eyeline) is 31.43°.
We can make a right triangle, where one of the cathetus is 11m, the adjacent angle to this cathetus is the complementary angle to the angle of depression, so we have:
Angle + 31.43° = 90°
Angle = 90° - 31.43° = 58.57°
Now, we can find the distance between the tree and the swingset as the other cathetus of our triangle, we can use the relation:
Tan(angle) = opposite cathetus/adjacent cathetus.
Tan(58.57) = X/11m
Tan(58.57)*11m = X = 17.9m