Two cars drive separately from two cities 500 kilometers apart. Car A travels 50 kilometers per hour, and after 1 hour, car B starts, and car B travels 40 kilometers per hour. How many hours will it take for the two cars to drive to meet each other?
两辆汽车分别从相距500千米的两个城市对开．甲车每时行50千米，行了1时后，乙车才出发，乙车每时行40千米．两辆汽车还需要行驶多少小时才能相遇．
<gadget id="calculator">50 * 1</gadget>
<output>50</output>

<gadget id="calculator">500 - 50</gadget>
<output>450</output>

<gadget id="calculator">50 + 40</gadget>
<output>90</output>

<gadget id="calculator">450 / 90</gadget>
<output>5</output>

<result>5</result>