Two people, A and B, start from a certain place and run in opposite directions on a circular track at the same time. A's speed is three times that of B's, and the distance between their first and second encounters is 100 meters. How many meters is the circular runway?
甲、乙两人在圆形跑道上，同时从某地出发沿相反方向跑步．甲的速度是乙的3倍，他们第一次与第二次相遇地点之间的路程是100米．环形跑道有多少米？
<gadget id="calculator">100 * 4</gadget>
<output>400</output>

<result>400</result>