A clothing factory made 3,000 sets of performance costumes for schools before the "Six Day" Children's Day, and completed 1,200 sets in the first 10 days. According to this calculation, how many days will it take to finish the rest? (Answer with proportional knowledge)
某服装厂在"六一"儿童节前为学校做3000套演出服，前10天完成了1200套．照这样计算，做完余下的还要多少天？(用比例知识解答)
<gadget id="calculator">3_000 - 1_200</gadget>
<output>1_800</output>

<gadget id="calculator">1_200 / 10</gadget>
<output>120</output>

<gadget id="calculator">1_800 / 120</gadget>
<output>15</output>

<result>15</result>