The engineering team repaired an 84-kilometer-long road. The original plan was to build 3 kilometers a day, but the actual repair was 4 kilometers a day. In this way, the task can be completed a few days earlier than planned?
工程队修一条长84千米的公路，原计划每天修3千米，实际每天修4千米，这样可以比计划提前几天完成任务？
<gadget id="calculator">84 / 3</gadget>
<output>28</output>

<gadget id="calculator">84 / 4</gadget>
<output>21</output>

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

<result>7</result>