Question 269335
From the first bit, we know that the father is (and has always been) 24 years older than the son, and from the second, we know that we're looking for a time when the father was three times as old. We have two equations:

f = s + 24
f = 3s

There are several ways to solve this. We can eliminate f and substitute back:

s + 24 = 3s
24 = 2s
s = 12, f = 36

Another option is to treble the first equation and eliminate s:

3f = 3s + 72
f  = 3s
2f = 72
f = 36