Master Zhang needs to install washing machines for three customers. Including the coming and going time, it takes 20 minutes for the Wang family and 40 minutes for the Zhao family. Li's needs 30 minutes. To minimize the total installation and waiting time for the three customers, please help Master Zhang arrange the installation order reasonably.
张师傅要为三位客户安装洗衣机，来去时间在内，王家需要20分钟，赵家需要40分钟．李家需要30分钟．要使三位客户安装和等候的时间总和最少，请你帮张师傅合理安排一下安装顺序．
<gadget id="calculator">20 * 3</gadget>
<output>60</output>

<gadget id="calculator">30 * 2</gadget>
<output>60</output>

<gadget id="calculator">60 + 60 + 40</gadget>
<output>160</output>

<result>160</result>