2) At your usual speed, a man goes down a river of 15 km of measure in 5 hours less than the time that he spends swimming in the same river wandering the opposite way. If he doubles his usual speed, he will go down a river spending only 1 hour less than the time spent in the return. Considering that the speed of the flow of the river keeps constant during the path which is your value in km/h? How you can make this exercise more challenging?