4 masters and apprentices processed a total of 720 parts in 9 hours, how many parts per hour per person on average?
师徒4人9小时共加工零件720个，平均每人每小时加工多少个零件？
<gadget id="calculator">720 / 4 / 9</gadget>
<output>20</output>

<result>20</result>