Two people, A and B, walk in opposite directions at the same time from the same point on a 400-meter-long circular runway. A walks 45 meters per minute, and B walks 35 meters per minute. How many minutes later did the two meet for the first time?
甲、乙二人在一个长400米的环形跑道上从同一点，同时反向而行，甲每分钟走45米，乙每分钟走35米．多少分钟后两人第一次相遇？
<gadget id="calculator">45 + 35</gadget>
<output>80</output>

<gadget id="calculator">400 / 80</gadget>
<output>5</output>

<result>5</result>