To process a batch of parts, A alone can complete it in 20 days, and B alone can complete this batch of parts every day (1/25). Now the two work together to complete the processing tasks of this batch of parts. A rests for 3 days, and B also rests for several days, so it takes 15 days to complete all the parts. How many days did B work from start to finish?
加工一批零件，甲单独做20天完成，乙单独做每天完成这批零件的(1/25)．现在两人合作完成这批零件的加工任务，甲中途休息了3天，乙中途也休息了若干天，这样用15天才全部完成．从开始到结束乙工作了多少天？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">15 - 3</gadget>
<output>12</output>

<gadget id="calculator">(1/20) * 12</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 / 25</gadget>
<output>1/25 = around 0.04</output>

<gadget id="calculator">(2/5) / (1/25)</gadget>
<output>10</output>

<result>10</result>