A man swims downstream 16 km and upstream 10 km taking 2 hours each time, what is the speed of the man in still water? Choose the correct answer:  A) 7.0  B) 8.2  C) 6.5  D) 7  E) 6

Rationale: "16 - - - 2 ds = 8 ? - - - - 1 10 - - - - 2 us = 5 ? - - - - 1 m = ? m = ( 8 + 5 ) / 2 = 6.5 answer : c"
Answer: C