Question 1023353
Call Dad's and son's age NOW, d and s.  Thus
d = 3s
In nine years,
d + 9 = 2(s + 9) 
Now substitute in for d here and get
3s + 9 = 2(s + 9)
3s + 9 = 2s + 18
and
s = 9 so that Dad is 
d = 27