The distance between the two cities is 640 kilometers. Cars A and B start from opposite sides of the two cities at the same time. Car A travels 75 kilometers per hour, and car B travels 85 kilometers per hour. How many hours later will the two cars meet?
两城相距640千米，甲、乙两车同时从两城相向出发．甲车每小时行75千米，乙车每小时行85千米．几小时后两车相遇？
<gadget id="calculator">75 + 85</gadget>
<output>160</output>

<gadget id="calculator">640 / 160</gadget>
<output>4</output>

<result>4</result>