Boats and Streams - General Questions

A boat whose speed in still water is 16 km/hr goes 80 km downstream. If the stream flows at 4 km/hr, how long does it take?

A man can row downstream at 41 km/hr and upstream at 9 km/hr. What is the speed of the stream?

A man can row downstream at 23 km/hr and upstream at 3 km/hr. What is the speed of the stream?

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 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?