Since, both Sonia and Ravi start at the same point and at the same time and go in the same direction. Sonia takes 18 minutes to drive one round of the circular field, while Ravi takes 12 minutes for the same.
Therefore, Sonia crosses starting point at 18 and 36 minutes.
And Ravi crosses the starting point at 12, 24 and 36 minutes.
Hence, Ravi (in his third round) and Sonia (in her second round) meat again at staring point in 36 minutes .
