It takes 5 seconds for a train to pass a road sign, 20 seconds to pass a 300-meter cave, and how many seconds to pass a 800-meter bridge.
一列火车经过一个路标需要5秒钟，通过300米的山洞要20秒钟，经过一座800米的大桥需要多少秒．
<gadget id="calculator">20 - 5</gadget>
<output>15</output>

<gadget id="calculator">300 / 15</gadget>
<output>20</output>

<gadget id="calculator">800 / 20</gadget>
<output>40</output>

<gadget id="calculator">40 + 5</gadget>
<output>45</output>

<result>45</result>