Xiaofang and Xiaoming are running on a circular track. They start from the same place and walk in opposite directions. Xiaofang's speed is 3 m/s, and Xiao Ming's speed is 5 m/s. After 100 seconds, the two met for the second time on the runway. How long is the circular runway in meters?
小芳和小明在环形跑道上跑步，两人从同一地点出发，反向而行，小芳的速度是3米/秒，小明的速度是5米/秒．经过100秒，两人在跑道上第2次相遇，这个环形跑道长多少米？
<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>