Father is four times as old as his son today. Six years ago,the product of the number denoting their ages was 252. Find their present ages.

1) F=4x
2) (F-6)(x-6)=252

combining by substitution...
(4x-6)(x-6)=252
which has a solution of x=12 (the other is -9/2 and is extraneous for our goal)
so the father is 48 and the son is 12