Answer:
4
Explanation:
An angle of elevation is the angle formed by a horizontal line and a line of sight to a point above the line.
An angle of depression is the angle formed by a horizontal line and a line of sight to a point below the line.
∠3 is an angle of elevation because it is formed by the line of sight that is above the horizontal line.
∠4 is an angle of depression because it is formed by the line of sight that is below the horizontal line.
∠5 is neither an angle of depression nor an angle of elevation because it is not formed by the horizontal line and the line of sight.
∠6 is an angle of elevation because it is formed by the line of sight that is above the horizontal line.
Therefore, the angle of depression is ∠4.