bridge is 2400 meters long. A train passes the bridge at a speed of 900 meters per minute. It takes 3 minutes from the front of the train on the bridge to the end of the train leaving the bridge. How long is the train?
一座大桥长2400米．一列火车以每分钟900米的速度通过大桥，从车头开上桥到车尾离开桥共需要3分钟，这列火车有多长？
<gadget id="calculator">3 * 900</gadget>
<output>2_700</output>

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

<result>300</result>