Boats and Streams - General Questions

A boat goes 38 km/hr downstream and 8 km/hr upstream. What is the speed of the boat in still water?

A boat whose speed in still water is 15 km/hr goes 40 km downstream. If the stream flows at 5 km/hr, how long does it take?

A boat whose speed in still water is 23 km/hr goes 84 km downstream. If the stream flows at 5 km/hr, how long does it take?

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

A man takes 7 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 8 km/hr, what is the speed of the stream?