The monthly personal maintenance allowance (PMA) for a family of an employee is determined by the average age of the family and size of the family. For every year of average age, the company pays Rs. 100 per member of the family. Jacob was drawing Rs. 5700 as PMA after he got married 6 years back. At present, he draws Rs. 7200 as PMA with his family of three after the birth of a son. What is the age of the son?