A train is 280 meters long and travels 20 meters per second. It takes 46 seconds for the whole train to pass through a tunnel. How long is this tunnel in meters?
一列火车全长280米，每秒钟行驶20米，全车通过一条隧道需46秒钟．这条隧道全长多少米？
<gadget id="calculator">20 * 46</gadget>
<output>920</output>

<gadget id="calculator">920 - 280</gadget>
<output>640</output>

<result>640</result>