Three vehicles came to the coal yard to load coal at the same time. It takes 4 hours and 30 minutes to fill a large truck, 1 hour and 30 minutes to fill a pickup truck, and 2 hours to fill a small truck. In order to minimize the total waiting time, how should they be arranged in the order of coal loading? How long is the shortest waiting time?
三辆车同时来到煤场装煤．大卡车装满需要4小时30分，皮卡车装满需要1小时30分，小货车装满需要2小时．为了使等候的总时间最短，应该如何安排它们装煤的顺序？等候的时间最短的多长时间？
<gadget id="calculator">1.5 * 3</gadget>
<output>4.5</output>

<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">4.5 + 4 + 4.5</gadget>
<output>13</output>

<result>13</result>