A job is completed in 15 days by A and B in cooperation, and 20 days by A alone. Now A and B cooperate in 6 days, and the rest of the work is done by B alone. How many days will it take to complete?
一件工作，甲乙二人合作15天完成，甲单独做20天完成，现在甲乙合作6天，剩下的工作由乙单独做，还需要几天完成？
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/15) * 6</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

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

<gadget id="calculator">(1/15) - (1/20)</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">(3/5) / (1/60)</gadget>
<output>36</output>

<result>36</result>