An aeroplane is moving at a constant altitude 'h'. At 10:00 AM, it is seen at an elevation of $$30^\circ$$. 1 minute later, it is observed at an elevation of $$60^\circ$$. If the speed of the plane is 960 km/h, then find 'h'.

A

15 km

B

20 km

C

12.46 km

D

13.86 km