The master processes 72 parts per hour, and the apprentice processes 48 parts per hour. The master first spends 2.5 hours instructing the apprentice, and then starts processing the parts. How many hours after the master works, the number of parts processed by the apprentice is the same?
师傅每小时加工零件72个，徒弟每小时加工零件48个，师傅先用2.5小时指导徒弟，然后再开始加工零件，师傅工作几小时后与徒弟加工的零件个数相同？
<gadget id="calculator">48 * 2.5</gadget>
<output>120</output>

<gadget id="calculator">72 - 48</gadget>
<output>24</output>

<gadget id="calculator">120 / 24</gadget>
<output>5</output>

<result>5</result>