A train is 180 meters long, and it takes 20 seconds for the entire train to pass through a 420-meter bridge. What is the speed of the train?
一列火车长180米，全车要通过420米的桥要20秒，则火车的速度是多少？
<gadget id="calculator">180 + 420</gadget>
<output>600</output>

<gadget id="calculator">600 / 20</gadget>
<output>30</output>

<result>30</result>