Boats and Streams - General Questions

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 goes 27 km/hr downstream and 3 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 4 km/hr, what is the speed of the stream?

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

A man takes 2 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?