Question 1170044
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The effective rate upstream is  {{{336/7}}} = 48 km/h,  and it is the difference 
of the boat rate in still water and the rate of current

    u - v = 48  km/h    (1)

   
The effective rate downstream is  {{{504/7}}} = 72 km/h,  and it is the sum 
of the boat rate in still water and the rate of current

    u + v = 72  km/h.   (2)



Adding equations (1) and (2), you find  u = 60 km/h  for the rate of the motorboat at still water.


Subtracting equations (1) and (2), you find  v = 12  km/h  for the rate of current.
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Solved.