Answer:
The line of sight distance is 1285.58 feet.
Step-by-step explanation:
The situation is illustrated in the figure attached.
From the figure we see that the altitude difference of the planes and the distance between them form a right triangle with one angle of 40° .
The line of sight between the two planes is the hypotenuse of the triangle.
The altitude difference of the planes is

Therefore, if we call
the line of sight distance, from trigonometry we have


Therefore, the line of sight distance (x) is 1285.58 feet.