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Hi
Jane is 12 years older than Kate
Let x and (x+12)represent kate and jane's age respectively
Question states***
 x = (x+12)/3
Solving for x
 3x = x+12
  2x = 12
   x = 6, Kate's age.  Jane is 18.    (6 + 12)
CHECKING our Answer***
 6 = 18/3