A man is running across a bridge.When he is 3/8 of the way accross, he hears a train coming
behind him. If he keeps running he will reach the end of the bridge at the same time with the train.
If he turns around and runs back, he will get to the beginning of the bridge at the same time with the train.
The man runs at a speed of 5mph, and there is no way to jump off the bridge. What is the speed of the train?