A and B work together to make 480 parts, A makes 48 parts per hour, and B makes 42 parts per hour. After a certain period of time, A leaves because of something, and B makes the remaining parts for 5 hours. , How many hours did A and B work together?
甲、乙两人合作做480个零件，甲每小时做48个，乙每小时做42个，两人合做了一定时间后，甲因有事离开，剩下的零件乙做了5小时才完成，求甲、乙两人合做了几小时？
<gadget id="calculator">240 / 100</gadget>
<output>12/5 = around 2.4</output>

<result>12/5 = around 2.4</result>