A project is completed in 20 days by A alone, and completed by B in 30 days alone. When they started working together, A rested for 3 days, and B also rested for a few days. Therefore, it took 16 days from beginning to end to complete the project. How many days did B rest in the middle?
一项工程，甲单独做20天完成，乙单独做30天完成，开始工作时两人合作，中间甲休息了3天，乙也休息了几天，所以从开始到结束，共用16天才完工，问乙中间休息了几天？
<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 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/30) * 16</gadget>
<output>8/15 = around 0.533333</output>

<gadget id="calculator">(8/15) - 1</gadget>
<output>-7/15 = around -0.466667</output>

<gadget id="calculator">(13/20) + (-7/15)</gadget>
<output>11/60 = around 0.183333</output>

<gadget id="calculator">(11/60) / (1/30)</gadget>
<output>11/2 = around 5.5</output>

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