There are two trains, the passenger cars are 200 meters long and travel 30 meters per second, and the trucks are 300 meters long and travel 20 meters per second. How many seconds does it take from meeting to passing by the wrong car?
有两列火车，客车长200米，每秒行30米，货车长300米，每秒行20米．从相遇到错车而过，需要多少秒．
<gadget id="calculator">300 + 200</gadget>
<output>500</output>

<gadget id="calculator">30 + 20</gadget>
<output>50</output>

<gadget id="calculator">500 / 50</gadget>
<output>10</output>

<result>10</result>