We know that
<span>If the slope of the angle from the vertex is positive, then it is an angle of elevation.</span>
<span>If the slope of the angle from the vertex is negative, then it is an angle of depression.</span>
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
