Uncle Fei is walking along a road parallel to the railway, walking 60 meters per minute, and a 300-meter-long train is coming towards him. It took 20 seconds from when the locomotive met Uncle Fei to when the train left him. Find the speed of the train.
费叔叔沿着一条与铁路平行的公路散步，每分钟走60米，迎面开过来一列长300米的火车．从火车头与费叔叔相遇到火车尾离开他共用了20秒．求火车的速度．
<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>