The master and the apprentice make 420 parts together, the master makes 32 parts per hour, and the apprentice makes 28 parts per hour, how many hours the two work together to complete the task.
师徒两人合做420个零件，师傅每小时做32个，徒弟每小时做28个，两个合做多少小时完成任务．
<gadget id="calculator">32 + 28</gadget>
<output>60</output>

<gadget id="calculator">420 / 60</gadget>
<output>7</output>

<result>7</result>