Dad and son practice running on a circular track with a circumference of 400 meters. They walk in the same direction from the same place at the same time. The father runs 120 meters per minute, and the son runs 80 meters per minute. After a few minutes, they meet for the first time?
爸爸和儿子在一个周长为400米环形跑道上练习跑步，他们同时从一地点同向而行，爸爸每分钟跑120米，儿子每分钟跑80米，几分钟后第一次他们相遇？
<gadget id="calculator">120 - 80</gadget>
<output>40</output>

<gadget id="calculator">400 / 40</gadget>
<output>10</output>

<result>10</result>