It takes 15 seconds for a train to pass through a 350-meter-long bridge, and 20 seconds to pass through a 550-meter-long tunnel. What is the speed of the train?
一列火车经过一座长350米的大桥用时15秒，经过一座长550米的隧道用时20秒，那么火车的车速是多少？
<gadget id="calculator">550 - 350</gadget>
<output>200</output>

<gadget id="calculator">20 - 15</gadget>
<output>5</output>

<gadget id="calculator">200 / 5</gadget>
<output>40</output>

<result>40</result>