A passenger rides on a train with a speed of 40 km / h. A train moving towards it passes it in 6 s

A passenger rides on a train with a speed of 40 km / h. A train moving towards it passes it in 6 seconds. What is the speed of the opposite train if its length is 100m. ?

1) Let us express the speed of a train with a passenger in m / s;
40 km / h 1000/3600 = 100/9 m / s;
2) The sum of the train speeds is:
100/6 = 50/3 m / s;
3) The speed of the oncoming train is:
50/3 – 100/9 = 50/9 m / s = 50/9 3600/1000 = 20 km / h;
Answer: The speed of the oncoming train is 20 km / h;