Hi

Let x and (x-3)represent the times for the 4kph and 5kph walkers respectively

Question states*** (Distance same for both:  D = r*t)

 4kphx = 5kph(x-3)

  15hr = x, time it took the walker at 4kp.  The distance is 4kph*15hr = 60k



CHECKING our Answer***

 4kph*15hr = 5kph*12 = 60k 

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