A processing group plans to process a batch of parts. If 20 parts are processed every day, it can be completed in 15 days. Actually, 100 parts are processed in 4 days. According to this calculation, how many days can the task be completed? (Solution by proportional method)
某加工小组计划加工一批零件，如果每天加工20个，15天可以完成，实际4天加工了100个．照这样计算，几天可完成任务？(用比例方法解)
<gadget id="calculator">20 * 15</gadget>
<output>300</output>

<gadget id="calculator">100 / 4</gadget>
<output>25</output>

<gadget id="calculator">300 / 25</gadget>
<output>12</output>

<result>12</result>