Xiao Zhang and Xiao Li are running on the circular track. They start from the same place and walk in the same direction. Xiao Zhang runs 4 meters per second, Xiao Li runs 6 meters per second, and they meet after 400 seconds. How many meters is the runway long? (answer in two ways)
小张和小李在环形跑道上跑步，两人从同一地点出发，同向而行．小张每秒跑4米，小李每秒跑6米，经过400秒两人相遇．跑道长多少米？(用两种方法解答)
<gadget id="calculator">4 * 400</gadget>
<output>1_600</output>

<gadget id="calculator">6 * 400</gadget>
<output>2_400</output>

<gadget id="calculator">1_600 + 2_400</gadget>
<output>4_000</output>

<result>4_000</result>