A train passes a 200-meter-long bridge at a speed of 20 meters per second and takes 21 seconds. How long is the train?
一列火车以每秒20米的速度通过一座长200米的大桥，共用21秒，这列火车长多少米？
<gadget id="calculator">20 * 21</gadget>
<output>420</output>

<gadget id="calculator">420 - 200</gadget>
<output>220</output>

<result>220</result>