Answer:
Define F as fathers age and S as sons age right now.
Then now they are
(1) 3S = F
and six years ago they were
(2) 5*(S-6) = F-6
calculate 5*(S-6)
5S - 30 = F-6
Subtract left and right side by -F
Add 30 to left and right side
5S - F = 24
Put (2) 3S = F into the equation above
5S - 3S = 24
2S = 24
S = 12
insert result in (2) 3S = F
3*12 = F
36 = F
Explanation:
So the son is 12 years, and the father is 36 years.