Question 669522
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Hi,
A boat takes 2hours to go 4 miles upstream.  {{{r = 4mi/2hr = 2mph}}}
It can go 8 miles downstream <u>in the same amount of time</u> of 2hrs.
  r - c = 4/2 = 2mph 
  <u>r + c = 8/2 = 4mph</u>   ||Adding EQs together to elminate c
   2r = 6mph
    r = 3mph  and  c = 1mph