Xinhua Bookstore shipped 540 copies of "Snow White". After 4 days of selling, there were 260 copies left. How many copies are sold per day on average?
新华书店运来540本《白雪公主》，卖了4天后，还剩260本．平均每天卖多少本？
<gadget id="calculator">540 - 260</gadget>
<output>280</output>

<gadget id="calculator">280 / 4</gadget>
<output>70</output>

<result>70</result>