The engineering team plans to repair 0.42 kilometers of roads every day, and the repairs will be completed in 20 days. Actually repair 0.7 kilometers per day. How many days can this be done in advance?
工程队计划每天修0.42千米的公路，20天修完．实际每天修0.7千米．这样可以提前几天修完？
<gadget id="calculator">20 / 0.7</gadget>
<output>28.571429</output>

<gadget id="calculator">0.42 * 28.571429</gadget>
<output>12</output>

<gadget id="calculator">20 - 12</gadget>
<output>8</output>

<result>8</result>