Question 431388
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Hi
Let x represent the rate of the boat in still water.
Question states***  Note t = D/r (times the same)
{{{ 7km/(x-6) = 20km/(x+6) }}}    | Cross Multiplying 
  7(x+6) = 20(x-6)
    162 = 13x
     x = 12.4615kmph
CHECKING our Answer***
  7/6.4615 = 20/18.4615 = 1.0833