The two masters and apprentices jointly processed 630 parts. The master processed 336 pieces in 8 hours, and the apprentice processed 21 pieces per hour. How many hours can the master and apprentice work together to complete the task?
师徒二人共同加工630个零件．师傅8小时加工了336个，徒弟每小时加工21个．师徒二人合做几小时可以完成任务？
<gadget id="calculator">336 / 8</gadget>
<output>42</output>

<gadget id="calculator">42 + 21</gadget>
<output>63</output>

<gadget id="calculator">630 / 63</gadget>
<output>10</output>

<result>10</result>