Question 384773
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Hi,         
Let x and 2x represent  their respective speeds
D = r*t
 3hr*x + 3hr*2x = 27km
     9hr*x = 27km
      x = 3kmph
  3kmph and 6kmph the speeds for the two boys.

CHECKING Our Anwser
 3hr*3kmph + 3hr*6kmph = 27km