A man swims downstream 48 km and upstream 18 km taking 3 hours each time, what is the speed of the man in still water?	Choices: A) 2 B) 8 C) 9 D) 11 E) 14

Rationale: "48 - - - 3 ds = 16 ? - - - - 1 18 - - - - 3 us = 6 ? - - - - 1 m = ? m = ( 16 + 6 ) / 2 = 11 answer : d"
Answer: D