The speed of the boat in still water in 12 kmph. It can travel downstream through 60 kms in 3 hrs. In what time would it cover the same distance upstream?
Choose the correct answer:
A) 8 hours	B) 6 hours	C) 4 hours	D) 15 hours	E) 6 hours

Rationale: "still water = 12 km / hr downstream = 60 / 3 = 20 km / hr upstream = > > still water = ( u + v / 2 ) = > > 12 = u + 20 / 2 = 4 km / hr so time taken in upstream = 60 / 4 = 15 hrs answer : d"
Answer: D