A man swims downstream 36 km and upstream 18 km taking 6 hours each time, what is the speed of the man in still water?	Choices
A) 4.5  B) 5.5  C) 6.5  D) 4.8  E) 2

Rationale: "36 - - - 6 ds = 6 ? - - - - 1 18 - - - - 6 us = 3 ? - - - - 1 m = ? m = ( 6 + 3 ) / 2 = 4.5 answer : a"
Answer: A