Two cars A and B are driving opposite each other from A and B at the same time. If A travels the whole journey, B travels 80% of the whole journey. If the two cars meet after 20 minutes, how many minutes before A arrives at the destination than B?
甲乙两车同时从A、B两地相对行驶，如果甲行全程时，乙行全程的80%，如果两车经20分钟相遇，那甲比乙提前多少分钟到达终点．
<gadget id="calculator">4 + 5</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">20 / (4/9)</gadget>
<output>45</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">20 / (5/9)</gadget>
<output>36</output>

<gadget id="calculator">45 - 36</gadget>
<output>9</output>

<result>9</result>