A project is completed in 20 days by A alone, 30 days by B alone, and two people work together. A rests for 3 days, and B rests for a certain number of days. It takes 16 days to complete the project. How many days does B rest?
一项工程，甲独做20天完成，乙独做30天完成，两人合做，其中甲休息了3天，乙休息了若干天，一共用了16天完成，乙休息了多少天．
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">16 - 3</gadget>
<output>13</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>