A passenger train running at the speed of 75 km/hr leaves the railway station 9 hours after a goods train leaves and overtakes it in 6 hours. The speed of the goods train is

The goods train's speed is 30 km/hr.

The passenger train runs 6 hours at 75 to overtake: 6 x 75 = 450 km.

When caught, the goods train has run 9 + 6 = 15 hours.

It covered the same 450 km in 15 hours.

Speed = 450/15 = 30 km/hr.