Two people, A and B, start from A and B at the same time and go towards each other. The speed of A is twice the speed of B. After the two met, they continued to move forward, and returned immediately after arriving at B and A respectively. It is known that the place where the two met for the second time is 12 kilometers away from the place where they met for the first time, so how many kilometers are the distance between A and B?
甲、乙两人分别从A、B两地同时出发，相向而行，甲的速度是乙的速度的2倍．两个相遇后继续往前走，各自到达B、A后立即返回．已知两人第二次相遇的地点距第一次相遇地点是12千米，那么A、B两地相距多少千米．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">12 / (2/3)</gadget>
<output>18</output>

<result>18</result>