Xiao Zhang and Xiao Li are running on the circular track. They start from the same place and walk in opposite directions. Xiao Zhang runs 8 meters per second, and Xiao Li runs 12 meters per second. After 40 seconds, the two meet, how many meters is the runway long?
小张和小立在环行跑道上跑步，两人从同一地点出发，反向而行．小张每秒钟跑8米，小立每秒跑12米．经过40秒两人相遇，跑道长多少米？
<gadget id="calculator">8 + 12</gadget>
<output>20</output>

<gadget id="calculator">20 * 40</gadget>
<output>800</output>

<result>800</result>