A section of the Hangzhou subway construction is 12 kilometers long, and 1.5 kilometers were completed in the first 3 days. According to this calculation, how many days will it take to complete this section?
杭州地铁施工某地段长12千米，前3天施工完成1.5千米，照这样计算，完成这一路段还要用多少天？
<gadget id="calculator">12 - 1.5</gadget>
<output>10.5</output>

<gadget id="calculator">1.5 / 3</gadget>
<output>0.5</output>

<gadget id="calculator">10.5 / 0.5</gadget>
<output>21</output>

<result>21</result>