Let the speed of train C be x km/h.
At 9 p.m. the train A will have covered a distance of 180 km.
For trains A and B relative speed = (90 – 60) = 30 km/h
Distance between them = 180 km
Time after which they meet =
= 6 hrs
For trains A and C relative speeds = (60 + x) km/h
Distance between them = 1080 km.
Time after which they meet =
hrs
As the time of meeting of all the three trains is the same, we have
= 6
or x = 120 km/h