Uncle Zhang has one day off after every 4 days of work, and Aunt Wang has one day off after every three days of work. Since they started working on January 2, 2010, how many days are their common rest days in January?
张叔叔每工作4天后休息一天，王阿姨每工作3天休息一天．从2010年1月2日起他们开始上班，则他们1月份共同的休息日有多少天．
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