Two people, A and B, are walking towards each other from two places A and B at the same time. A's speed is 30 kilometers per hour, and B's speed is 20 kilometers per hour. After the two meet, they continue to move forward. Return immediately after arriving at A. It is known that the place where the two met for the second time is 20 kilometers away from the place where they first met. Then, how many kilometers are the distance between A and B?
甲、乙二人分别从A、B两地同时相向而行，甲的速度是每小时30千米，乙的速度是每小时20千米，二人相遇后继续行进，甲到B地、乙到A地后立即返回．已知二人第二次相遇的地点距第一次相遇的地点是20千米，那么，A、B两地相距多少千米．
<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">2 * 3</gadget>
<output>6</output>

<gadget id="calculator">2 + 3</gadget>
<output>5</output>

<gadget id="calculator">6 / 5</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">(6/5) - 1</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(3/5) - (1/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">20 / (2/5)</gadget>
<output>50</output>

<result>50</result>