In one hour, a boat goes 7 km along the steram and 5 km against the stream. The speed of the boat in still waer (in km/hr) is: Choose the correct choice from the following answers:	A) 2	B) 4	C) 6	D) 12	E) 15

Rationale: "sol . speed in still water = 1 / 2 ( 7 + 5 ) kmph = 6 kmph . answer c"
Answer: C