bridge is 2400 meters long. When a train passes the bridge, it travels 900 meters per minute. It takes 3 minutes from the front of the train to the bridge to the rear of the train leaving the bridge. How long is this train?
一座大桥2400米，一列火车通过大桥时每分钟行900米，从车头开上桥到车尾离开桥共需要3分钟．这列火车长多少米？
<gadget id="calculator">3 * 900</gadget>
<output>2_700</output>

<gadget id="calculator">2_700 - 2_400</gadget>
<output>300</output>

<result>300</result>