The distance between A and B is 4800 meters. A and B start from A and B at the same time and walk toward each other. If A walks 60 meters per minute, B walks 100 meters per minute. The speed remains the same, but A changes direction when starting, that is, two people start at the same time and in the same direction. May I ask: How long can B catch up with A after starting off?
A、B两地相距4800米，甲、乙两人分别从A、B两地同时出发，相向而行，如果甲每分钟走60米，乙每分钟走100米，如果甲、乙两人的速度大小不变，但甲出发时改变方向，即两个人同时、同向出发．请问：乙出发后多久可以追上甲？
<gadget id="calculator">100 - 60</gadget>
<output>40</output>

<gadget id="calculator">4_800 / 40</gadget>
<output>120</output>

<result>120</result>