The workers installed a batch of utility poles, 12 poles per day, which could be completed in 30 days. How many days can it be completed if 6 more are installed every day? (Solve with ratio)
工人们安装一批电线杆，每天安装12根，30天可以完成．如果每天多安装6根，几天能够完成？(用比例解)
<gadget id="calculator">12 * 30</gadget>
<output>360</output>

<gadget id="calculator">12 + 6</gadget>
<output>18</output>

<gadget id="calculator">360 / 18</gadget>
<output>20</output>

<result>20</result>