For a project, A works alone for 2 days, and then cooperates with B for 7 days. In this way, half of the whole project is completed. It is known that A needs to do 2 days of work, and B needs to do 3 days to complete. If this work is done by A on the first day, B on the second day, A on the third day, and B On the 4th day, A works on the 5th day, and B works on the 6th day... so how many days will it take to complete the work?
一项工程，甲先单独做2天，然后与乙合作7天．这样才完成全工程的一半，已知甲做2天的工作量乙需要做3天才能完成，如果这件工作由甲做第1天，乙做第2天，甲做第3天，乙做第4天，甲做第5天，乙做第6天…，那么完成工作需要多少天？
<result>33</result>