A father's age is 30 years more than his son's age. Ten years hence, the father's age will become three times the son's age at that time. What is the son's present age (in years)?

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?