Answer:
1633.3 meters
Explanation:
-Given the angle of depression is 31°, and the plane's height above the ground is 1400m.
-We use the Law of Sines to determine the distance between the plane and the rock.
-The angle of elevation from the rock to the plane is(corresponds to the plane's altitude):

#Now, using Sine Law;

Hence, the direct distance between the plane and the rock is 1633.3 meters