Both start, A leaves, B finishes the rest in d days: after how many days A left

The same question, asked 2 times: 18 Jul 2023 S2*, 18 Sep 2025 S2. Every wording below, oldest first.

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Question 1
18 Jul 2023 S2
72 $A and B can do a piece of work in 5 days and 10 days, respectively. They began the work together but A left after some days and B finished the remaining work in 8 days. After how many days did A leave?$
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Question 2
18 Sep 2025 S2
55 $A and B can finish a certain job in 28 and 35 days, respectively. They started working together, but A left after a while, and B managed to complete the remaining work in 17 days. How many days did A work before leaving?$
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Question 1