project alone takes 30 days to complete, and B alone takes 20 days to complete. Now the two are working together, but B took a few days off in the middle, and it took 18 days from the start to the end of the work. How many days did B take a break?
一项工程，甲单独做要30天完成，乙单独做要20天完成．现两人合作，但中途乙休息了几天，结果从开工到结束一共用了18天，请问乙休息了几天？
<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/30) * 18</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(2/5) / (1/20)</gadget>
<output>8</output>

<gadget id="calculator">18 - 8</gadget>
<output>10</output>

<result>10</result>