A man can row at 12 km/hr in still water. It takes him 4 times as long to row upstream as to row downstream on the same river. The speed of the stream is:

The speed of a motorboat in still water is 15 km/h. It travels 30 km downstream and returns to the starting point in a total time of 4 hours 30 minutes. What is the speed of the stream (in km/h)?

The speed of a motorboat in still water is 15 km/h. It travels 30 km downstream and returns to the starting point in a total time of 4 hours and 30 minutes. What is the speed of the stream (in km/h)?