Xiao Ming and Xiao Liang are running on the circular track, starting from the same place at the same time, and running in opposite directions. Xiao Ming's speed is 4 m/s, Xiao Liang's speed is 6 m/s, and they meet after 40 seconds. How long is the circular runway in meters?
小明和小亮在环形跑道上跑步，从同一地点同时出发，反向而行．小明的速度是4米/秒，小亮的速度是6米/秒，经过40秒两人相遇．环形跑道长多少米？
<gadget id="calculator">4 + 6</gadget>
<output>10</output>

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

<result>400</result>