Install a batch of electric poles, install 12 poles every day, and finish the installation in 30 days. If you install 15 poles every day, how many days will it take to finish the installation?
装一批电杆，每天装12根，30天装完，如果每天装15根，只要多少天装完？
<gadget id="calculator">12 * 30</gadget>
<output>360</output>

<gadget id="calculator">360 / 15</gadget>
<output>24</output>

<result>24</result>