It takes 21 seconds for a train to pass through a 120-meter-long bridge, and 17 seconds to pass through an 80-meter-long tunnel at the same speed. How long is the body of this train?
一列火车通过120米长的桥要21秒钟，以同样的速度通过80米长的隧道要17秒钟．这列火车的车身长多少米？
<gadget id="calculator">120 - 80</gadget>
<output>40</output>

<gadget id="calculator">21 - 17</gadget>
<output>4</output>

<gadget id="calculator">40 / 4</gadget>
<output>10</output>

<gadget id="calculator">10 * 21</gadget>
<output>210</output>

<gadget id="calculator">210 - 120</gadget>
<output>90</output>

<result>90</result>