The distance between A and B is 660 km. A train of passenger cars and a train of freight trains travel towards each other from two stations A and B at the same time. The passenger train travels 90 kilometers per hour and the freight train travels 75 kilometers per hour. After how many hours did the two cars meet?
甲乙两站相距660千米．一列客车和一列货车同时从甲乙两站相向而行，客车每小时行90千米，货车每小时行75千米．经过多少两车小时相遇？
<gadget id="calculator">90 + 75</gadget>
<output>165</output>

<gadget id="calculator">660 / 165</gadget>
<output>4</output>

<result>4</result>