Xinhua Bookstore shipped 300 copies of "Snow White", selling an average of 9 copies per day, and now there are 30 copies left. How many days has it been sold?
新华书店运来300本《白雪公主》，平均每天卖9本，现在还剩30本．已经卖了多少天？
<gadget id="calculator">300 - 30</gadget>
<output>270</output>

<gadget id="calculator">270 / 9</gadget>
<output>30</output>

<result>30</result>