A road was built with a total length of 12 kilometers, and 1.5 kilometers were repaired in 3 days. According to this calculation, how many days will it take to complete the road? (Solve with ratio)
修一条公路，总长12千米，开工3天修了1.5千米．照这样计算，修完这条公路还需要多少天？(用比例解)
<gadget id="calculator">12 - 1.5</gadget>
<output>10.5</output>

<gadget id="calculator">3 * 10.5</gadget>
<output>31.5</output>

<gadget id="calculator">31.5 / 1.5</gadget>
<output>21</output>

<result>21</result>