A train is 250 meters long and travels 30 meters per second. It takes the train 50 seconds to pass through a tunnel. How long is the tunnel?
一列火车长250米，每秒钟行30米，这列火车通过一个隧道用了50秒，这个隧道长多少米？
<gadget id="calculator">30 * 50</gadget>
<output>1_500</output>

<gadget id="calculator">1_500 - 250</gadget>
<output>1_250</output>

<result>1_250</result>