I take it angle of depression is measured from the horizontal view of the airplane?
Drawing this out will give you a right angled triangle, with a smaller right angled triangle contained within this, both with a side of 37,000 ft.
Using the tan rule, we get the first town to be 59212.38 ft away from the point directly below the airplane. Repeating this for the second town and we get this town to be 9225.14 ft away from the point below the airplane.
If we subtact the second value from the first, we then get the distance between the towns to be 49987ft to the nearest foot.
This is presuming I have not done it some overly complicated way again
Hope this helps