<PRE><B>Question 283714</B>
Let speed of boat in still water  be x

Speed upstream will be x-4

Speed of boat down stream will be x+4

Time upstream = 6/ x-4      ( Time = distance / rate)

Time downstream = 12/x+4

Both these times are same

6/x-4 = 12 / x+4

6(x+4)=12(x-4)

6x+24=12x-48

6x=72

x= 12 mph the speed of boat in still water

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