The master and the apprentice work together to make 800 parts. The master processes 50 parts per hour, and the apprentice processes 40 parts per hour.
师徒二人合做800个零件，师傅每时加工50个，徒弟每时加工40个，师傅有事耽误了2时，完成了任务后，师傅工作了多少时？
<gadget id="calculator">40 * 2</gadget>
<output>80</output>

<gadget id="calculator">800 - 80</gadget>
<output>720</output>

<gadget id="calculator">40 + 50</gadget>
<output>90</output>

<gadget id="calculator">720 / 90</gadget>
<output>8</output>

<result>8</result>