The municipal construction needs to install lighting facilities for the "Middle Ring Line", and the first team of workers is responsible for installing a batch of electric poles. Pack 12 sticks every day, and it can be completed in 20 days. If 15 sticks are installed every day, how many days can the task be completed in advance?
市政建设要为"中环线"安装照明设施，第一小队工人负责安装一批电杆．每天装12根，20天可以完成．如果每天装15根，能够提前几天完成任务？
<gadget id="calculator">20 / 15</gadget>
<output>4/3 = around 1.333333</output>

<gadget id="calculator">12 * (4/3)</gadget>
<output>16</output>

<gadget id="calculator">20 - 16</gadget>
<output>4</output>

<result>4</result>