Question 392246
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Hi
Let x and (x + 6kmph) represent the speeds traveling 63km and 72km respectively
Question States***total time of trip 3hr.  t = D/r
 63/x  + 72/(x+6) = 3  |Multiplying each term by x(x+6) so as all denominators= 1
 63(x+6) + 72x = 3x(x+6)
 63x + 6*63 + 72x = 3x^2 + 18x
   3x^2 -117x - 378 = 0
  3(x^2 - 39x - 126) = 0
factoring
  (x+3)(x-42) = 0
  (x+3) = 0   |tossing out negative solution
  (x-42) = 0
    x = 42kmph, speed of train while traveling 63kmph, the original average speed

CHECKING our Answer ***
  63km/42kmph + 72km/48kmph = 1.5hr + 1.5hr =  3hr