Question 843111
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Hi,
What is Al's rowing rate {{{highlight_green(x)}}}in still water?
t = D/r
*** {{{5km/(x+4kph) + 5km/(x-4kph) = 3hr }}}|Multiplying thru by (x+40(x-4) so as all denominators = 1
  5(x-4) + 5(x+4) = 3(x+4)(x-4)
      10x = 3x^2 - 48
     3x^2 - 10x - 48 = 0
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
{{{x = (10 +- sqrt( 676 ))/(6) }}}
{{{x = (10 +- 26)/(6) }}}
   x = 6,   (tossing out negative solution for unit measure)
  6kph is Al's rowing rate in still water
CHECKING our answer***
 5/10 + 5/2  = 5/10 + 25/10 = 30/10 = 3hr
Wish You the Best in your Studies.