There is a batch of parts to be processed, and it takes 8 hours for Master Wang to complete it alone, and 6 hours for Master Li to complete it alone. If Master Wang does it for 2 hours first, and then Master Li does it alone, how many hours will it take for Master Li to finish it?
有一批零件要加工，王师傅单独做要8小时完成，李师傅单独做要6小时完成．如果王师傅先做2小时，再由李师傅单独做，李师傅还要几小时才能完成？
<result>4</result>