Two people, A and B, are doing a job. At the same time, the work efficiency ratio of A and B is 3:5. After the two worked together for 3 days, B left for something, and A completed the task in another 2 days. How many days will it take if the two work together from the beginning until the completion?
甲、乙两人做一件工作，在同一时间内甲、乙二人的工作效率比是3：5．两人共同工作3天后，乙有事离开，甲又用2天完成了任务．如果一开始二人就合作直到完成，需要多少天？
<gadget id="calculator">3 + 5</gadget>
<output>8</output>

<gadget id="calculator">8 * 3</gadget>
<output>24</output>

<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<gadget id="calculator">24 + 6</gadget>
<output>30</output>

<gadget id="calculator">30 / 8</gadget>
<output>15/4 = around 3.75</output>

<result>15/4 = around 3.75</result>