In one hour, a boat goes 9 km along the stream and 5 km against the stream. The speed of the boat in still water (in km/hr) is:
Select the correct option
A) 2
B) 4
C) 7
D) 12
E) 15

Rationale: "sol . speed in still water = 1 / 2 ( 9 + 5 ) kmph = 7 kmph . answer c"
Answer: C