Two towns A and B are connected by a regular bus service with a bus leaving in either direction every T minutes. A man cycling with a speed of `20 km h^(-1)` in the direction A to B notices that a bus goes past him every 18 min in the direction of his motion, and every 6 min in the opposite direction. What is the period T of the bus service and with what speed (assumed constant) do the buses ply on the road ?

Explanation

T = 9 min, speed = 40 km/h.
Jint : `upsilon T//(upsilon - 20) = 18, upsilon T//(upsilon+20)=6`