A man swims downstream 36 km and upstream 18 km taking 3 hours each time, what is the speed of the man in still water?	Choose the correct choice
A) 7 B) 8 C) 9 D) 2 E) 4
36 --- 3 DS = 12   ? ---- 1   18 ---- 3 US = 6   ? ---- 1 M = ?   M = (12 + 6)/2= 
<gadget id="calculator">(12 + 6)/2</gadget>
<output>9</output>
9   Answer:9
<result>C</result>
A man swims downstream 36 km and upstream 18 km taking 3 hours each time, what is the speed of the man in still water?