A train passes through a 300-meter-long tunnel. It is known that it takes 9 seconds from the front of the train to enter the tunnel to the rear of the train. After another 10 seconds, the train just passes through the tunnel. Find the total length of the train.
一列火车，通过300米长的隧道，已知由车头开始进入洞口到车尾进入洞口共需要9秒，又过了10秒钟，火车刚好全部通过隧道，求这列火车的全长．
<gadget id="calculator">300 / 10</gadget>
<output>30</output>

<gadget id="calculator">10 + 9</gadget>
<output>19</output>

<gadget id="calculator">30 * 19</gadget>
<output>570</output>

<gadget id="calculator">570 - 300</gadget>
<output>270</output>

<result>270</result>