The body of a train is 900 meters long and the speed is 60 kilometers per hour. There are two tunnels on the railway. It takes 3 minutes for the train to enter the first tunnel from the front to leave the first tunnel at the rear, and enter the second tunnel from the front. It takes 4 minutes from the tunnel to the rear of the car to leave the second tunnel, and 9 minutes from the front of the car to the first tunnel to the rear of the car to leave the second tunnel. How many meters are there between the two tunnels?
一列火车的车身长900米，行驶速度为每小时60千米，铁路上有两个隧洞，火车从车头进入第一个隧洞到车尾离开第一个隧洞用3分钟，从车头进入第二个隧洞到车尾离开第二个隧洞用4分钟，从车头进入第一个隧洞到车尾离开第二个隧洞共用9分钟，两座隧洞之间相距多少米．
<gadget id="calculator">60_000 / 60</gadget>
<output>1_000</output>

<gadget id="calculator">1_000 * 9</gadget>
<output>9_000</output>

<gadget id="calculator">1_000 * 3</gadget>
<output>3_000</output>

<gadget id="calculator">3_000 - 900</gadget>
<output>2_100</output>

<gadget id="calculator">1_000 * 4</gadget>
<output>4_000</output>

<gadget id="calculator">4_000 - 900</gadget>
<output>3_100</output>

<gadget id="calculator">9_000 - 2_100 - 3_100 - 900</gadget>
<output>2_900</output>

<result>2_900</result>