Boats and Streams - General Questions

A boat goes 28 km/hr downstream and 4 km/hr upstream. What is the speed of the boat in still water?

A boat goes 18 km/hr downstream and 4 km/hr upstream. What is the speed of the boat in still water?

A boat whose speed in still water is 21 km/hr goes 52 km downstream. If the stream flows at 5 km/hr, how long does it take?

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?

A boat goes 13 km/hr downstream and 9 km/hr upstream. What is the speed of the boat in still water?