First you have to figure out the length of the track:

r is the half of the diameter:
200ft : 2 = 100ft

= 200

≈
628,31
The athlete has to run ca. 5280ft for one mile:
5280 : 628,31≈8,4
The athlete has to run 8,4 laps
4x - 24 = -2x + 30
4x + 2x = 30 + 24
6x = 54
x = 9
answer: the number is 9