It takes 15 seconds for a 300-meter train to pass a telegraph pole. It took the train 75 seconds to pass through a tunnel at the same speed. How long is the tunnel?
一列300米的火车经过一根电线杆用了15秒．这列火车以同样的速度经过一条隧道用了75秒，那么这条隧道长多少米？
<gadget id="calculator">300 / 15</gadget>
<output>20</output>

<gadget id="calculator">20 * 75</gadget>
<output>1_500</output>

<gadget id="calculator">1_500 - 300</gadget>
<output>1_200</output>

<result>1_200</result>