A train crew was cleaning out a rail tanker that had been emptied of its contents. They rinsed the rail car out with scalding hot water through a port of the bottom of the rail car. When they were finished and had drained the water out they shut the valve of the port and went home for the day. During the night the temperature droppe d and it was very cold outside. When they came back to the work the next night something happens to the rail car!

Distance covered = speed x timethe distance traveled going against the stream = distance traveled with the stream.therefore it is the speed and the time that are the variables.as he travels the same distance both ways, speed x time is the same for each way.going upstream his speed is 4 kph; going downstream his speed is 6 kph.therefore we have two simultaneous equations: time upstream x 4 = time downstream x 6time upstream + time downstream = 60 minutestherefore we have the equation: time upstream = 6/10 hour, time downstream therefore = 4/10 hour.distance traveled at 4km/hr in 6/10 hour = 24/10 = 2.4km.check: distance traveled at 6km/hr in 4/10 hour = 24/10 = 2.4km.