Four persons A, B, C and D run along a 36 km long circular path. They start their race from the same starting point and they start at the same time. A, B, C and D runs at the speed of 6 km/hr, 9 km/hr, 12 km/hr and 15 km/hr respectively. After how much time will they meet again at the starting point?
1
36 hours
2
12 hours
3
6 hours
4
18 hours