Question 657995
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Hi,
The oldest girl is three times older than the youngest age {{{highlight(x)}}}. 
The middle girl is 3 years older than the youngest.
youngest:  x
middle girl: x+ 3
oldest girl: 3x
Question states***The sum of their age is 28 
  x + (x+3) + 3x = 28
     5x = 25
      x = 5, the age of the youngest.  The middle girl is 8 

and (oldest is 15)
{{{ 5 + 8 + 15 = 28}}}