In 5 hours person A will cover 5*3 = 15 miles.

           person B will cover 5*7 = 35 miles,  which is one entire circumference of 20 miles plus the same 15 miles: 35 = 20 + 15.

           person C will cover 5*11 = 55 miles, which is TWO TIMES entire  circumference of 20 miles plus the same 15 miles: 55 = 2*20 + 15.



So, in 5 hours all three of them will be at the same point on the circumference.



To that time person A will be on the way making his first lap;

             person B will complete his first lap and will be on the way making his 2-nd lap;

         and person C will complete his TWO laps and will be on the way making his 3-rd lap.

    For two bodies that started simultaneously from one point and move uniformly along the circle (along the closed path) of 
    the circumference S in the same direction with different speeds/rates  and ,  > , the time from the start till the moment
    when the faster body will catch the slower body is this condition


         = S:     the difference between the covered distanses is exactly equal to the circumference.


    It is also the condition for the time duration between any two consecutive catching moments.