THREE PIPES A, B AND C CAN FILL A CISTERN IN 6 HOURS. AFTER WORKIN...

14. Three pipes A, B and C can fill a cistern in 6 hours. After working at it together for 2 hours, C is closed and A and B can fill the remaining part in 7 hours. The number of hours taken by C alone to fill the cistern is: (1) 12 (2) 14 (3) 16 (4) 18