Two points A and B lie along a line at a distance of 120km apart. P and Q start at the same time from A and B with speeds 40km/h and 60km/h respectively. They travel towards each other and after their meeting for the first time, they then go in reverse directions and also interchange their speeds. These speeds are continued in their further journey. After reaching their respective starting points, they reverse their directions of travel and proceed towards each other again. The time taken by them to meet each other 2nd time is