Two people, A and B, start from A and B at the same time and walk towards each other. The ratio of the speed of A and B is 5:4. After they meet, they continue to move forward. A arrives at B, and B returns to A immediately. It is known that the distance between the places where the two meet twice is 20 kilometers, find the distance between A and B.
甲、乙二人分别从A、B两地同时出发，相向而行，甲乙速度之比为5：4，二人相遇后继续前进，甲到B地，乙到A地都立即返回．已知二人两次相遇的地点之间相距20千米，求A、B两地的距离．
<gadget id="calculator">5 + 4</gadget>
<output>9</output>

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

<gadget id="calculator">(5/9) * 3</gadget>
<output>5/3 = around 1.666667</output>

<gadget id="calculator">1 - (5/9)</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">(5/3) - 1 - (4/9)</gadget>
<output>2/9 = around 0.222222</output>

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

<result>90</result>