On an oval runway with a circumference of 400 meters, two people, A and B, ride bicycles from two points 300 meters apart and walk towards each other along the runway. After meeting, they continue to move forward. It is known that A's cycling speed is 4 m/s, and B's cycling speed is 6 m/s. Then when they met 6 times, how many seconds did the two ride at least?
在周长为400米的椭圆跑道上，甲、乙两人分别骑自行车从相距300米的两点同时出发沿着跑道相向而行，相遇后两人各自继续前进．已知甲的骑车速度是4米/秒，乙的骑车速度是6米/秒．那么相遇6次时，两人至少骑了多少秒．
<gadget id="calculator">400 * 5</gadget>
<output>2_000</output>

<gadget id="calculator">100 + 2_000</gadget>
<output>2_100</output>

<gadget id="calculator">4 + 6</gadget>
<output>10</output>

<gadget id="calculator">2_100 / 10</gadget>
<output>210</output>

<result>210</result>