A man swims downstream 28 km and upstream 16 km taking 4 hours each time, what is the speed of the man in still water?  Choose the correct choice from the following.
A) 6.5
B) 8.6
C) 7.5
D) 9.2
E) 5.5
28 --- 4 DS = 7   ? ---- 1   16 ---- 4 US = 4   ? ---- 1 M = ?   M = (7 + 4)/2= 
<gadget id="calculator">(7 + 4)/2</gadget>
<output>11/2 = around 5.5</output>
5.5   Answer: 5.5
<result>E</result>
A man swims downstream 28 km and upstream 16 km taking 4 hours each time, what is the speed of the man in still water?