Xiao Ming and Xiao Hua are running on the school's circular track. They start from the same place and walk in opposite directions. Xiao Ming runs 5 meters per second, and Xiao Hua runs 3 meters per second. After 100 seconds, the two meet for the second time. How many meters is the runway long?
小明和小华在学校的环形跑道上跑步，两人从同一地点出发，反向而行．小明每妙跑5米，小华每秒跑3米，经过100秒两人第二次相遇．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>