A project can be completed in 20 days if A alone does it; B can complete it in 30 days if B does it alone. Now the two are working together, A rests for 3 days in the middle, and B rests for several days, and it takes 16 days to complete. How many days did B rest?
一件工程，甲独做，20天可以完成；乙独做，30天可以完成．现在两人合做，中间甲休息了3天，乙休息了若干天，结果经过16天才完成．问乙休息了几天？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/20) * 13</gadget>
<output>13/20 = around 0.65</output>

<gadget id="calculator">1 - (13/20)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(7/20) / (1/30)</gadget>
<output>21/2 = around 10.5</output>

<gadget id="calculator">16 - (21/2)</gadget>
<output>11/2 = around 5.5</output>

<result>11/2 = around 5.5</result>