It takes 5 seconds for a train to pass a road sign, 20 seconds to pass a 300-meter bridge, how many seconds does it take to cross a 800-meter tunnel.
一列火车通过一个路标，用了5秒，通过一座300米的桥用了20秒，它穿越一条800米的隧道用多少秒．
<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>