If 2 times Mary's present age is 27 years more than 5 times Dia's present age, and 7 times Dia's present age is 9 years less than Mary's present age, then what is the difference (in years) between the ages of Mary and Dia?

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?