The store shipped 60 boxes of fruit, sold 42 boxes, and the rest will be sold out in 3 days. How many boxes are sold per day on average?
商店运来60箱水果，卖了42箱，剩下的要在3天卖完，平均每天要卖多少箱？
<gadget id="calculator">60 - 42</gadget>
<output>18</output>

<gadget id="calculator">18 / 3</gadget>
<output>6</output>

<result>6</result>