It takes 6 hours to travel from A to B by express train and 8 hours by slow train. If two cars drive from A and B oppositely at the same time, they can meet at a distance of 30 kilometers from the midpoint. How many kilometers is the distance between A and B?
从甲地到乙地快车需6小时，慢车需8小时．如果两车同时从甲、乙两地相对开出，可以在距离中点30千米处相遇，甲、乙两地的距离是多少千米？
<gadget id="calculator">4 + 3</gadget>
<output>7</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">(4/7) - (3/7)</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">2 / (1/7)</gadget>
<output>14</output>

<gadget id="calculator">30 * 14</gadget>
<output>420</output>

<result>420</result>