A road construction team repaired a section of road. It was originally planned to pave 4.2 kilometers per day and finish paving in 56 days. The actual extra shop (1/7) per day, how many days earlier than the original plan was the actual completion? (Solution with proportional knowledge)
一个筑路队修一段公路，原计划每天铺4.2千米，56天铺完．实际每天多铺(1/7)，实际比原计划提前多少天完工？(用比例知识解)
<gadget id="calculator">4.2 * 56</gadget>
<output>235.2</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">4.2 * (1/7) * 56</gadget>
<output>33.6</output>

<gadget id="calculator">33.6 - 235.2</gadget>
<output>-201.6</output>

<gadget id="calculator">235.2 + (-201.6)</gadget>
<output>33.6</output>

<gadget id="calculator">4.2 * (1/7)</gadget>
<output>0.6</output>

<gadget id="calculator">4.2 + 0.6</gadget>
<output>4.8</output>

<gadget id="calculator">33.6 / 4.8</gadget>
<output>7</output>

<result>7</result>