help word problem

f = 9s

In three years :

   f+3  = 6 (s+3)      Sub in the red equation

 

  9s +3  = 6 (s+3)

   9s + 3 = 6s + 18

   3s      = 15

    s = 5  y/o     then f = 9s = 45 y/o

A father is 9 times as old as his son. In three years, the father will be 6 times as old as his son.
How old is the son?

 

Son = x       Father = 9x

x + 3                9x + 3

(9x + 3) / (x + 3) = 6

x = 5