If a boat can cover 250 km downstream and 150 km upstream in 5 hours each, then how much distance will a wooden object flowing in the river cover in 6 hours?

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)?