A, B, and C working alone can finish constructing a house in 4, 8, and 12 hours respectively. A starts alone and works for 1 hour. He is then joined by B and they work together for 1 hour. Finally C joins them and they all work together to finish the work. If they start working at 9 am, at what time will they finish? Choose the correct option:  A) 11:12 am  B) 11:32 am  C) 11:49 am  D) 12:07 pm  E) 12:35 pm
A completes 1/4 of the job each hour.   B completes 1/8 of the work each hour.   C completes 1/12 of the work each hour.   A completes 1/4 of the work in the first hour.   Working together, A and B complete another 3/8 for a total of 5/8.   Working together, A, B, and C can complete 11/24 of the work each hour.   To complete 3/8, the time required is (3/8) / (11/24) = 9/11 hours.   The work will be completed at 11:00 plus 9*60/11 minutes which is about 11:49 am.   The answer is 11:49 am.
<result>C</result>
A, B, and C working alone can finish constructing a house in 4, 8, and 12 hours respectively. A starts alone and works for 1 hour. He is then joined by B and they work together for 1 hour. Finally C joins them and they all work together to finish the work. If they start working at 9 am, at what time will they finish?