A worker accepts the task of making 480 parts, and completes 120 parts in 3 days. Later, his work efficiency is doubled. How many days did he spend making this batch of parts?
一个工人接受制作480个零件的任务，工作3天完成了120个，后来工作效率提高了2倍，他制作这批零件共用了多少天．
<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<gadget id="calculator">480 - 120</gadget>
<output>360</output>

<gadget id="calculator">120 / 3</gadget>
<output>40</output>

<gadget id="calculator">40 * 3</gadget>
<output>120</output>

<gadget id="calculator">360 / 120</gadget>
<output>3</output>

<gadget id="calculator">3 + 3</gadget>
<output>6</output>

<result>6</result>