There are 3 people A, B, and C. The distance from point P to point Q is 3 kilometers, and each person can walk at a speed of 3 kilometers per hour. There are two bicycles at point P. If you use bicycles, the speed can reach 15 kilometers per hour, but each bicycle can only be ridden by one person. Ask how to make all three people reach the location Q in the shortest time?
有A、B、C共3人，从地点P到地点Q的距离为3千米，每个人可以每小时3千米的速度步行．在地点P有两辆自行车，如果使用自行车，速度可达到每小时15千米，但每辆自行车只能一个人骑．问怎样才能在最短的时间内使三人都到达地点Q？
<result>28</result>