Two people, A and B, are walking towards each other from places A and B at the same time. A travels 4.5 kilometers per hour, and B travels 3 kilometers per hour. After the two met for the first time, they continued to move forward. When A arrives at point B, he returns immediately on the same route and at the same speed, and when B arrives at point A, he immediately returns on the same route. The two walked for 4 hours from the beginning to the second encounter. Find the distance between AB and AB in kilometers?
甲、乙两人分别从A、B两地同时相向而行，甲每小时行4.5千米，乙每小时行3千米．两人第一次相遇后继续向前走．甲到达B地立即按原路原速度返回，乙到达A地后也立即按原路返回．两人从开始到第二次相遇时共走了4小时．求AB两地相距多少千米？
<gadget id="calculator">4.5 + 3</gadget>
<output>7.5</output>

<gadget id="calculator">4 / 3</gadget>
<output>4/3 = around 1.333333</output>

<gadget id="calculator">7.5 * (4/3)</gadget>
<output>10</output>

<result>10</result>