Two people, A and B, are running from the same place around a 400-meter circular track at the same time, walking in the same direction. A walks 6 meters per second and B walks 4 meters per second. After how many seconds can A catch up to B for the first time?
甲、乙两人同时从同一地点围绕400米的环形跑道跑步，同向而行．甲每秒走6米、乙每秒走4米．经过多少秒甲可以第一次追到乙？
<gadget id="calculator">6 - 4</gadget>
<output>2</output>

<gadget id="calculator">400 / 2</gadget>
<output>200</output>

<result>200</result>