We develop two different right triangles in which the opposite side to the given angle of depression is 1500 ft and the length of the runway is the y.
(45°) --> tan (45°) = 1500 ft / y₁
y₁ = 1500 ft
(42⁰) --> tan (42⁰) = 1500 ft / y₂
y₂ = 1665.92 ft
Finding the difference between two y's, the answer would be 165.92 ft.
