10. If a man rows at 5 km/hr in still water and 3.5 km/hr against the current, his rate along the current is :

11. A man can row at 5 km/hr in still water and the velocity of current is 1 km/hr. It takes him 1 hour to row to a place and back. How far is the place :

12. A man can row with the stream at 11 km/hr and against the stream at 8 km/hr. The speed of the stream is :