Boats and Streams - General Questions

A boat goes 19 km/hr downstream and 9 km/hr upstream. What is the speed of the boat in still water?

A boat whose speed in still water is 18 km/hr goes 40 km downstream. If the stream flows at 2 km/hr, how long does it take?

A man can row downstream at 25 km/hr and upstream at 9 km/hr. What is the speed of the stream?

A man can row downstream at 14 km/hr and upstream at 6 km/hr. What is the speed of the stream?

A man takes 17 times as long to row a distance upstream as to row the same distance downstream. If the speed of the boat in still water is 9 km/hr, what is the speed of the stream?