residential area plans to use 40 migrant workers to complete the task of laying gas pipelines in two weeks. After the migrant workers worked for 2 days, 20 more people were added. If the work efficiency of each migrant worker is the same, how many days in advance can the community use gas.
一个居民小区计划用40名民工，两周时间完成煤气管道的铺设任务．民工工作了2天后，又增加了20人，若每个民工的工作效率相同，这个小区可以提前多少天用上煤气．
<gadget id="calculator">7 * 2</gadget>
<output>14</output>

<gadget id="calculator">1 / 14</gadget>
<output>1/14 = around 0.071429</output>

<gadget id="calculator">(1/14) * 2</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">1 - (1/7)</gadget>
<output>6/7 = around 0.857143</output>

<gadget id="calculator">20 / 40</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/14) * (1/2)</gadget>
<output>1/28 = around 0.035714</output>

<gadget id="calculator">(1/14) + (1/28)</gadget>
<output>3/28 = around 0.107143</output>

<gadget id="calculator">(6/7) / (3/28)</gadget>
<output>8</output>

<gadget id="calculator">14 - 2 - 8</gadget>
<output>4</output>

<result>4</result>