The Sichuan Earthquake Relief Deployment Plan built 24,000 simple houses within 30 days after the earthquake. In fact, 20% of the task was completed in the first 4 days. How many days can the task be completed in advance?
四川抗震救灾部署计划在震后30天内搭建简易房24000间，实际前4天就完成了任务的20%，这样可以提前多少天完成任务？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">4 / (1/5)</gadget>
<output>20</output>

<gadget id="calculator">30 - 20</gadget>
<output>10</output>

<result>10</result>