Answer:
13,000 ft.
Explanation:
X -------10960----------C---------------D---------------Y
The entire race (from X to Y) is 7 miles. There are 5,280 ft. in one mile, so 7 miles is 36960 ft.
If we subtract 10,960 from 36,960, then we get the distance from C to Y.
36960-10960 = 26000
They tell you D is at the midpoint between C and Y
So if we divide 26,000 by 2, then we know the distance from C to D and from D to Y.
26000/2 = 13000
The checkpoints are C and D, so the distance between them is 13,000 ft.