It takes 9 seconds for a train to pass a worker standing on the side of the railway, and it takes 54 seconds to pass a 900-meter-long bridge at the same speed. What is the length of the train?
一列火车通过站在铁路边的一名工人用时9秒，它以同样的速度通过一座长900米的大桥用时54秒，这列火车的车长是多少．
<gadget id="calculator">54 - 9</gadget>
<output>45</output>

<gadget id="calculator">900 / 45</gadget>
<output>20</output>

<gadget id="calculator">20 * 9</gadget>
<output>180</output>

<result>180</result>