Xiaohong, Xiaolan, and Xiaogang go to the office to read their homework, and the required time is 6 minutes, 4 minutes, and 9 minutes respectively. How can the teacher arrange to minimize the total waiting time?
小红、小兰、小刚到办公室看作业，需要的时间分别是6分钟、4分钟、9分钟，老师怎样安排才能使等的时间总和最少多少．
<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<gadget id="calculator">12 + 12 + 9</gadget>
<output>33</output>

<result>33</result>