Two towns A and B are connected by a regular bus service with a bus leaving in either direction every T minutes with same speed. A man cycling with speed of 20km/h in the direction A to B, notices that a bus goes past him every t1=18 minutes in the direction of motion, and every t2=6 minutes in the opposite direction. What is the period T of the bus service? Assume that velocity of cyclist is less than velocity of bus.