Eighteen years ago, a man was three times as old as his son. Now the man is twice as old as his son. The sum of the present ages of the man and his son is

The sum of their present ages is 108 years.

Let son = s, man = 2s now.

18 years ago: 2s - 18 = 3(s - 18).

2s - 18 = 3s - 54, so s = 36.

Man = 72, son = 36, sum = 72 + 36 = 108.