The master and apprentice plan to make 264 parts, the master makes 18 parts per hour, and the apprentice makes 12 parts per hour. After the master has done 54 tasks, the apprentice will cooperate with the master. How many hours can the master and apprentice work together to complete the task?
师徒两人计划做264个零件，师傅每小时做18个，徒弟每小时做12个．师傅做了54个后，徒弟与师傅合做，师徒两人共同工作几小时才能完成任务？
<gadget id="calculator">264 - 54</gadget>
<output>210</output>

<gadget id="calculator">18 + 12</gadget>
<output>30</output>

<gadget id="calculator">210 / 30</gadget>
<output>7</output>

<result>7</result>