A train is 900 meters long. It takes 1.5 minutes to pass a big tree on the side of the road, and 3.5 minutes to pass a bridge at the same speed. What is the length of the bridge in meters?
一列火车长900米，从路边的一棵大树旁通过用了1.5分钟，以同样的速度通过一座大桥用了3.5分钟，这座大桥的长度是多少米．
<gadget id="calculator">900 / 1.5</gadget>
<output>600</output>

<gadget id="calculator">600 * 3.5</gadget>
<output>2_100</output>

<gadget id="calculator">2_100 - 900</gadget>
<output>1_200</output>

<result>1_200</result>