The engineering team built a 420-kilometer road, which was originally planned to be completed in 28 days, but actually built 5 kilometers more roads every day. How many days earlier than the original plan was the actual completion?
工程队修一条长420千米的公路，原计划28天完成，实际每天多修路5千米，实际比原计划提前几天完成？
<gadget id="calculator">420 / 28</gadget>
<output>15</output>

<gadget id="calculator">15 + 5</gadget>
<output>20</output>

<gadget id="calculator">420 / 20</gadget>
<output>21</output>

<gadget id="calculator">28 - 21</gadget>
<output>7</output>

<result>7</result>