Angles of elevation / depression should be only 30°, 45°, 60°.

Angle of Depression

It is the angle formed by the line of sight with the horizontal line when the object is below the horizontal level.

In figure, the eye is at point O and the position of the object is P therefore OP is the line of sight which makes an angle XOP from Horizontal line. 
Hence the angle the angle of depression = XOP.

Note: While solving the problems of height and distance following points must be noted.
(i)    First of all read the question carefully and draw the figure.
(ii)    In right triangle, trigonometric ratio of known angles (sine, cosine, tangent etc.) are express in the term of known side.
(iii)    From given figure, it is clear that the angle of elevation of ‘O’ with respect to ‘P’ is equal to the angle of depression of ‘P’ with respect to O’. i.e. the angle of elevation of one object is equal to the angle 
         of depression of the other object with respect to the first object.