Speed of boat in still water is 9 km/hr. Stream speed initially is 2 km/hr but it increases by 3 km/hr after every hour. Find the time after which boat will come back to the position where it started.(in hour)
1
5(5/8)
2
4(7/8)
3
5(3/8)
4
4(3/4)
5
None of these