A passenger car and a truck travel in opposite directions from the midpoint of A and B at the same time. After 3 hours, the bus arrives at point A, and the truck is still 20 kilometers away from point B. If the speed ratio of the truck and the bus is 7:9, how many kilometers are there between A and B?
客车和货车同时从甲、乙两地的中点向相反方向行驶．3小时后，客车到达甲地，货车离乙地还有20千米．如果货车和客车的速度比是7：9，甲、乙两地相距多少千米？
<gadget id="calculator">7 / 9</gadget>
<output>7/9 = around 0.777778</output>

<gadget id="calculator">1 - (7/9)</gadget>
<output>2/9 = around 0.222222</output>

<gadget id="calculator">20 / (2/9)</gadget>
<output>90</output>

<gadget id="calculator">90 * 2</gadget>
<output>180</output>

<result>180</result>