bridge is 2,800 meters long. A train travels 800 meters per minute when passing the bridge. How long is this train?
一座大桥长2800米，一列火车通过大桥时每分钟行800米，从车头开上桥到车尾离开桥共用4分．这列火车长多少米．
<gadget id="calculator">4 * 800</gadget>
<output>3_200</output>

<gadget id="calculator">3_200 - 2_800</gadget>
<output>400</output>

<result>400</result>