What is the speed of the stream if a canoe rows upstream at 4km/hr and downstream at 12km/hr  Choose the correct choice from the following answers.
A) 1 kmph B) 4 kmph C) 3 kmph D) 2 kmph E) 1.9 kmph

Rationale: "sol . speed of stream = 1 / 2 ( 12 - 4 ) kmph = 4 kmph . answer b"
Answer: B