Solution: The distance x (m) is the same twice, and the time difference between the two times is 8+2+5= 15 minutes. Suppose it takes t minutes for the first time, then it takes (t- 15) minutes for the second time.

So there is: t*50=(t- 15)*60.

T=80 minutes.

So x = 50 * 80 = 4000m.