A delivery car is loaded with 900 boxes of apples, and after delivering to 28 retail stores, there are still 60 boxes left. How many boxes of apples are delivered to each retail store on average?
一辆送货汽车装了900箱苹果，送完28个零售店后，还剩下60箱，平均每个零售店送了几箱苹果？
<gadget id="calculator">900 - 60</gadget>
<output>840</output>

<gadget id="calculator">840 / 28</gadget>
<output>30</output>

<result>30</result>