Chapter 13, Trigonometric Ratios and Functions - 13.1 Use Trigonometry with Right Triangles - 13.1 Exercises - Problem Solving - Page 857: 33

$651.92 ft$ The angle increases the final depth gradually.

Here, we have $\tan 15^{\circ}=\dfrac{d}{1500}$ This gives: $ d \approx 1500 tan 15^{\circ}$ and $d \approx 401.92 ft$ Thus, $401.92 ft+ 250 ft =651.92 ft$ Hence, the angle increases the final depth gradually.