Xiaohong and Xiaoming walk in opposite directions from the same place on a 400-meter circular runway. Xiaohong walks 45 meters per minute, and Xiao Ming walks 55 meters per minute. How many minutes later will they meet?
小红和小明在400米的环形跑道上从同一地点向相反方向行走，小红每分钟走45米，小明每分钟走55米，两人几分钟后相遇？
<gadget id="calculator">45 + 55</gadget>
<output>100</output>

<gadget id="calculator">400 / 100</gadget>
<output>4</output>

<result>4</result>