Cars A and B start from AB, which is 520 kilometers apart, at the same time and drive toward each other. Car A travels 60 kilometers per hour, and Car B travels 70 kilometers per hour. How many hours after the two cars set off do they meet?
甲、乙两车分别从相距520千米的AB两地同时出发，相向而行，甲车每小时行60千米，乙车每小时行70千米，两车出发后几小时相遇？
<gadget id="calculator">60 + 70</gadget>
<output>130</output>

<gadget id="calculator">520 / 130</gadget>
<output>4</output>

<result>4</result>