Fangfang and Yuanyuan run along the school's circular runway. They run from the same place in opposite directions. Fangfang runs 4 meters per second, and Yuanyuan runs 6 meters per second. After 40 seconds, the two meet. How long is the school runway in meters? ?
方方和圆圆沿学校环形跑道跑步，他俩从同一地点往相反方向跑去，方方每秒跑4米，圆圆每秒跑6米，经过40秒两人相遇，学校跑道长多少米？
<gadget id="calculator">4 + 6</gadget>
<output>10</output>

<gadget id="calculator">10 * 40</gadget>
<output>400</output>

<result>400</result>