Answer:
[tex]2\sqrt{2} \text{ mi}[/tex]
Step-by-step explanation:
See the attached image for a picture of the situation. The angle of depression lets you find the angle next to it but inside the triangle. It, too, must measure 45 degrees.
That means the triangle is an isosceles triangle (two legs of equal length).
Apply the Pythagorean Theorem.
[tex]x^2+x^2=4^2\\2x^2=16\\x^2=18\\x=\sqrt{8}=2\sqrt{2}\approx 2.83\text{ mi}[/tex]
