The distance between the two places is 240 kilometers. Two cars, A and B, leave from the two places respectively and drive toward each other. Car A travels 20 kilometers per hour. If car A and car B leave at the same time, after traveling for 4 hours, the two cars meet; if car A leaves 3 hours earlier than car B, how many hours will car A meet B?
两地相距240千米，甲、乙两车分别从这两地开出，相向而行，甲车每小时行20千米．如果甲车与乙车同时开出，行了4小时，两车相遇；如果甲车比乙车早3小时开出，甲车行多少小时与乙车相遇．
<gadget id="calculator">20 * 3</gadget>
<output>60</output>

<gadget id="calculator">240 - 60</gadget>
<output>180</output>

<gadget id="calculator">240 / 4</gadget>
<output>60</output>

<gadget id="calculator">60 - 20</gadget>
<output>40</output>

<gadget id="calculator">20 + 40</gadget>
<output>60</output>

<gadget id="calculator">180 / 60</gadget>
<output>3</output>

<gadget id="calculator">3 + 3</gadget>
<output>6</output>

<result>6</result>