A woman swims downstream 45 km and upstream 15 km taking 3 hours each time, what is the speed of the woman in still water?  Choose the correct choice from the following answers.
A) 10  B) 12  C) 14  D) 16  E) 18

Rationale: 45 - - - 3 ds = 15 ? - - - - 1 15 - - - - 3 us = 5 ? - - - - 1 m = ? m = ( 15 + 5 ) / 2 = 10 answer : a
Answer: A