‘P’ began a business by investing Rs. 24000. After (x + 2) months, ‘Q’ entered with Rs. 18000, and again after (x + 2) more months, ‘R’ joined them by investing Rs. 30000. If the profit-sharing ratio among them at the end of the year was 8:6:5 respectively, then after how many months from the beginning did ‘R’ join?