For a project, if A works for 5 days first, then B works for 3 days to complete the task; if B works for 9 days first, and A works for 3 days, the task is just completed. Now if A works for 4 days first, then B will continue Do, then how many days will it take B to complete the task?
一项工程，如果甲先做5天，乙接着做3天刚好完成任务；如果乙先做9天，甲接着做3天，也刚好完成任务，现在如果甲先做4天，再由乙接着做，那么乙还需几天才能完成任务？
<gadget id="calculator">9 - 3</gadget>
<output>6</output>

<gadget id="calculator">5 - 3</gadget>
<output>2</output>

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

<gadget id="calculator">1 * 3</gadget>
<output>3</output>

<gadget id="calculator">3 + 3</gadget>
<output>6</output>

<result>6</result>