A woman swims downstream 54 km and upstream 6 km taking 6 hours each time, what is the speed of the woman in still water?
Answers
A) 2 B) 3 C) 4 D) 5 E) 6

Rationale: "54 - - - 6 ds = 9 ? - - - - 1 6 - - - - 6 us = 1 ? - - - - 1 m = ? m = ( 9 + 1 ) / 2 = 5 answer : d"
Answer: D