The distance between A and B is 168 kilometers. Two cars, A and B, are driving from A to B at the same time. A travels 39 kilometers per hour, and B travels 24 kilometers per hour. A stops on the way for some reason. After a while, when car B arrives at point B, car A travels another 12 kilometers to reach point B. How long did car A stop on the way?
甲、乙两地相距168千米，A、B两车同时从甲地开往乙地，A车每小时行39千米，B车每小时行24千米，A车因故在途中停了一会儿，当B车到达乙地时，A车再行12千米才能到达乙地，问A车在途中停了多长时间？
<gadget id="calculator">168 / 24</gadget>
<output>7</output>

<gadget id="calculator">168 - 12</gadget>
<output>156</output>

<gadget id="calculator">156 / 39</gadget>
<output>4</output>

<gadget id="calculator">7 - 4</gadget>
<output>3</output>

<result>3</result>