A factory needs to produce 321 parts. It has been produced for 6 days, and there are still 21 parts left unfinished. How many parts are produced on average per day?
一个工厂要生产321个零件，已经生产了6天，还剩下21个零件没完成，平均每天生产多少个？
<gadget id="calculator">321 - 21</gadget>
<output>300</output>

<gadget id="calculator">300 / 6</gadget>
<output>50</output>

<result>50</result>