It takes 2 workers a total of 12 hours to build a giant machine with each worker working at the same rate. If 3 workers start to build the machine at 11:00 AM, and one extra worker per hour is added beginning at 2:00 PM, at what time will the machine be complete?  Choose the correct option.
A) 4:30  B) 4:45  C) 5:00  D) 5:15  E) 5:30
2 workers build 1/12 of a machine in one hour.   1 worker builds 1/24 of a machine in one hour.   In the first 3 hours, 3 workers build 3*(1/24)*3=9/24 of a machine   From 2:00 to 3:00, 4 workers build another 4/24. The total is 13/24.   From 3:00 to 4:00, 5 workers build another 5/24. The total is 18/24.   From 4:00 to 5:00, 6 workers build another 6/24. The total is 24/24.   The machine is complete at 5:00.   The answer is 5:00.
<result>C</result>
It takes 2 workers a total of 12 hours to build a giant machine with each worker working at the same rate. If 3 workers start to build the machine at 11:00 AM, and one extra worker per hour is added beginning at 2:00 PM, at what time will the machine be complete?