At both ends of a diameter of a circular runway with a circumference of 400 meters, two persons A and B ride a bicycle at a speed of 6 meters per second and 4 meters per second while driving clockwise along the circumference. How long does it take? A catches up with B for the second time?
在周长为400米的圆形跑道的一条直径的两端，甲、乙两人分别以每秒6米和每秒4米的速度骑自行车同时沿圆周按顺时针方向行驶，经过多长时间甲第二次追上乙？
<gadget id="calculator">6 - 4</gadget>
<output>2</output>

<gadget id="calculator">400 / 2 / 2</gadget>
<output>100</output>

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

<gadget id="calculator">100 + 200</gadget>
<output>300</output>

<result>300</result>