Manoj starts a business with Rs.40,000. After 2 months, Nayan joined him with Rs.60,000. Ajit joined them after some more time with Rs.1,20,000. At the end of the year, out of a total profit of Rs.3,75,000, Ajit gets Rs.1,50,000 as his share. How many months after Nayan joined the business, did Ajit join?