Lao Li is walking along the railway. He walks 60 meters per minute. A 300-meter-long train is coming towards him. It takes him 20 seconds to meet the front of the train and separate from the rear of the train. Find the speed of the train in meters per minute.
老李沿着铁路散步，他每分钟走60米，迎面过来一列长300米的火车，他与车头相遇到与车尾相离共用了20秒，求火车的速度是每分钟多少米．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">60 * (1/3)</gadget>
<output>20</output>

<gadget id="calculator">300 - 20</gadget>
<output>280</output>

<gadget id="calculator">280 / (1/3)</gadget>
<output>840</output>

<result>840</result>