Boats and Streams - General Questions

A man can row downstream at 24 km/hr and upstream at 18 km/hr. What is the speed of the stream?

A man rows at 8 km/hr in still water. The river flows at 4 km/hr. How long will he take to row 54 km upstream and come back?

A boat goes 48 km/hr downstream and 12 km/hr upstream. What is the speed of the boat in still water?

A man rows at 10 km/hr in still water. The river flows at 2 km/hr. How long will he take to row 6 km upstream and come back?

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?