After 15 years, a man will be just four times as old as he was 15 years ago. What is his present age?

At the time of marriage, a man was 6 years older than his wife. 12 years after the marriage, his age became 65 times the age of his wife. What were their ages (in years) at the time of marriage?

The total age of father and son at present is 40 years. After 16 years, the age of the father will be twice the age of his son. What is the present age of the son?