A man can row 30 km upstream and 55 km downstream in the same amount of time as he can row 38.5 km downstream and 37.5 km upstream. Find the ratio of the rowing speed in still water to the speed of the current.

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)?