(4) In such types of questionswhere two trains start towards eachother and cross each other to reachtheir respective destinations, thereis a relation between the speed andtime of the two trains (trains A andB in this case), i.e.
SpeedoftrainA
SpeedoftrainB
=√
TimetakenbytainB
TimetakenbyTrainA
Thus, Let the speed of Train A = SA, and the time taken by Train A=5
1
7
hSpeed of Train B = 54 km/h, andthe time taken by Train B = 9