Lili Supermarket shipped 840 apples, each packed in a box of 4, and packed in a box of 10 boxes. How many boxes of these apples can be packed in total?
丽丽超市运来840个苹果，每4个一装一盒，每10盒装一箱，这些苹果一共可以装多少箱？
<gadget id="calculator">840 / 4 / 10</gadget>
<output>21</output>

<result>21</result>