A bridge is 3,500 meters long. When a train passes the bridge, it travels 950 meters per minute. It takes 4 minutes from the front of the train to the bridge to the end of the train leaving the bridge. How long is this train?
一座大桥长3500米，一列火车通过这座大桥时每分钟行驶950米，从车头开上桥到车尾离开桥一共用了4分钟．这列火车长多少米哦？
<gadget id="calculator">4 * 950</gadget>
<output>3_800</output>

<gadget id="calculator">3_800 - 3_500</gadget>
<output>300</output>

<result>300</result>