The garment factory plans to make 840 sets of clothes, but has already made 390 sets, and the rest will be completed within 9 days. How many sets are made on average per day?
服装厂计划做840套服装，已经做了390套，剩下的要在9天内完成，平均每天做多少套？
<gadget id="calculator">840 - 390</gadget>
<output>450</output>

<gadget id="calculator">450 / 9</gadget>
<output>50</output>

<result>50</result>