A project, A, B cooperation 6 days to complete. If A works in 3 days first, and B can complete it in 7 days, how many days will it take for B to complete the project alone?
一项工程，甲、乙合作6天完成．如果甲先做3天，乙再做7天也可以完成，乙单独完成这项工程需几天？
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">3 / 1 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">(1/6) * (3/4)</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">1 / (1/8)</gadget>
<output>8</output>

<result>8</result>