On a 400-meter circular runway, A and B start from the starting line at the same time and run with their backs. A runs 4 meters per second, and B runs 6 meters per second. When they first meet on the starting line, they are already How many seconds did it run?
在400米的环形跑道上，甲、乙两人同时从起跑线出发，背向而跑，甲每秒跑4米，乙每秒跑6米，当他们第一次相遇在起跑线上时，他们已跑了多少秒？
<gadget id="calculator">6 - 4</gadget>
<output>2</output>

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

<result>200</result>