Xiaohong and Xiaoli are running on the circular track. They start from the same place and walk in the opposite direction. Xiaoli runs 3 meters per second, and Xiaohong runs 5 meters per second. After 100 seconds, the two meet for the second time. How long is the circular runway in meters?
小红和小丽在环形跑道上跑步，两人从同一地点出发反向而行，小丽每秒跑3米，小红每秒跑5米，经过100秒两人第二次相遇．环形跑道长多少米？
<gadget id="calculator">5 + 3</gadget>
<output>8</output>

<gadget id="calculator">100 / 2</gadget>
<output>50</output>

<gadget id="calculator">8 * 50</gadget>
<output>400</output>

<result>400</result>