A and B walk in opposite directions from the centers of A and B at the same time. When A arrives at A after 3 hours, B is still 3 kilometers away from B. It is known that B's speed is A's (4/ 5) Find the distance between A and B.
甲、乙两人同时从A、B两地的中心向相反的方向步行，3小时后甲到达A地时，乙离B地还有3千米，已知乙的速度是甲的(4/5)，求A、B两地间的距离．
<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<gadget id="calculator">15 + 12 + 3</gadget>
<output>30</output>

<result>30</result>