The speed of the boat in still water in 12 kmph. It can travel downstream through 39 kms in 3 hrs. In what time would it cover the same distance upstream?
Choose the correct choice from the following:
A) 3.5 hours	B) 6 hours	C) 4 hours	D) 5 hours	E) 6 hours

Rationale: "still water = 12 km / hr downstream = 39 / 3 = 13 km / hr upstream = > > still water = ( u + v / 2 ) = > > 12 = u + 13 / 2 = 11 km / hr so time taken in upstream = 39 / 11 = 3.5 hrs answer : a"
Answer: A