The following question has three statements. Study the question and the statements and decide which of the statement(s) is necessary to answer the question.

What is the difference of ages of Rohit’s wife and his son?

I. At the time of marriage Rohit's age was 25 years.

II. The average age of Rohit and Rohit's wife at the time of marriage was 24 years.

III. The difference between the present ages of Rohit and his son is 27 years.