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Hi
Paul is 15 years younger then Ken
Let x and (x-15) represent Ken and Paul's ages NOW respectively
Write as we Read*** in five years...
 [x+5] = 2[(x-15) + 5]
solving for x
 x + 5 = 2x - 20
    25 = x, Ken's age now, Paul is now 10.  Paul be in four years will be 14.
CHECKING our Answer***in five years...
  30 = 2*15