The speed of the boat in still water in 12 kmph. It can travel downstream through 42 kms in 3 hrs. In what time would it cover the same distance upstream? Pick one.
A) 8 hours  B) 6 hours  C) 4.2 hours  D) 5 hours  E) 6 hours

Rationale: "still water = 12 km / hr downstream = 42 / 3 = 14 km / hr upstream = > > still water = ( u + v / 2 ) = > > 12 = u + 14 / 2 = 10 km / hr so time taken in upstream = 42 / 10 = 4.2 hrs answer : c"
Answer: C