Xiao Zhang and Xiao Li are running on a 400-meter circular track. They start from the same place at the same time and walk in opposite directions. Xiao Zhang runs 4 meters per second, and Xiao Li runs 6 meters per second. How many seconds did it take for the two to meet for the first time?
小张和小李在400米的环形跑道上跑步，两人同时从同一地点出发，反向而行．小张每秒跑4米，小李每秒跑6米，经过多少秒两人第一次相遇？
<gadget id="calculator">4 + 6</gadget>
<output>10</output>

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

<result>40</result>