The master and the apprentice process the same kind of machine parts. Within 8 hours, the master processed 13 boxes and the apprentice processed 9 boxes. The apprentice processed 48 less than the master. How many parts per box?
师傅和徒弟加工同一种机器零件，8小时内，师傅加工了13盒，徒弟加工了9盒．徒弟共比师傅少加工48个．每盒装多少个零件？
<gadget id="calculator">13 - 9</gadget>
<output>4</output>

<gadget id="calculator">48 / 4</gadget>
<output>12</output>

<result>12</result>