There is only one pump in the car repair shop, and it takes 7 minutes to pump up a tricycle, 5 minutes to pump up a large cart, and 3 minutes to pump up a bicycle. If there are three cars at the same time, one for each. How to arrange the order of pumping so that the sum of the waiting time of these three cars is the least? How long does it take at least to wait for all three cars to run out of gas?
修车铺只有一个打气筒，给一辆三轮车打足气需要7分钟，给一辆大板车打足气需要5分钟，给一辆自行车打足气需要3分钟．如果同时来了三种车各一辆．该怎样安排打气的顺序，使得这三辆车等候的时间总和最少？最少等待多长时间三辆车都能打完气？
<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<gadget id="calculator">9 + 10 + 7</gadget>
<output>26</output>

<result>26</result>