A man swims downstream 54 km and upstream 18 km taking 3 hours each time, what is the speed of the man in still water?  Select:  A) 2  B) 8  C) 9  D) 10  E) 12
54 --- 3 DS = 18   ? ---- 1   18 ---- 3 US = 6   ? ---- 1 M = ?   M = (18 + 6)/2= 
<gadget id="calculator">(18 + 6)/2</gadget>
<output>12</output>
12   Answer: 12
<result>E</result>
A man swims downstream 54 km and upstream 18 km taking 3 hours each time, what is the speed of the man in still water?