A project, A, B, and C can complete all the tasks in 7 days by cooperation. Now, after 3 days of cooperation, A is transferred away, and B and C continue to cooperate for 5 days to complete the project. Ask A how many days it will take to complete it alone.
一工程，甲、乙、丙三人合作7天可完成全部任务，现在三人合作3天后，甲调走，乙、丙继续合作5天后完工，问甲一人独做需要几天才能完成．
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">1 - (3/7)</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">(4/7) / 5</gadget>
<output>4/35 = around 0.114286</output>

<gadget id="calculator">(1/7) - (4/35)</gadget>
<output>1/35 = around 0.028571</output>

<gadget id="calculator">1 / (1/35)</gadget>
<output>35</output>

<result>35</result>