we know that
If the slope of the angle from the vertex is positive, then it is an angle of elevation.
If the slope of the angle from the vertex is negative, then it is an angle of depression.
The angle of elevation is congruent to the angle of depression because they are alternate interior angles
in the picture
∠ 1 is the angle of elevation from submarine to the boat
∠2 is the angle of depression from boat to submarine
∠3 is the angle of elevation from boat to the lighthouse
∠4.is the angle of depression from the lighthouse to the boat
therefore
the answer is
∠2 is the angle of depression from boat to submarine