A bridge is 1,500 meters long. A train travels 20 meters per second on average. It takes 85 seconds for the train to get on the bridge and completely exit the bridge. How long is the train in meters?
一座桥全长1500米，一列火车平均每秒行20米，火车上桥到完全出桥用去85秒，这列火车全长多少米？
<gadget id="calculator">20 * 85</gadget>
<output>1_700</output>

<gadget id="calculator">1_700 - 1_500</gadget>
<output>200</output>

<result>200</result>