The length of the railway between the two stations is 400km. A train of freight trains and a train of passenger trains leave oppositely from these two stations at the same time, the passenger trains travel 110 km per hour, and the freight trains travel 90 km per hour. After how many hours did the two cars meet?
两站间的铁路长400km．一列货车和一列客车同时从这两站相对开出，客车每小时行110km，货车每小时行90km．经过几小时两车相遇？
<gadget id="calculator">110 + 90</gadget>
<output>200</output>

<gadget id="calculator">400 / 200</gadget>
<output>2</output>

<result>2</result>