Three lathe workers A, B, and C are going to turn seven parts on three lathes with the same efficiency. The time required to process each part is 4, 5, 6, 6, 8, 9, and 9 minutes respectively. The three of them started working at the same time. Question: After a reasonable division of labor, how many minutes can be used to complete all the parts?
甲、乙、丙三名车工准备在同样效率的三个车床上车出七个零件，加工各零件所需要的时间分别为4、5、6、6、8、9、9分钟．三人同时开始工作．问：经过合理分工，最少经过多少分钟可以车完全部零件？
<gadget id="calculator">8 + 5</gadget>
<output>13</output>

<gadget id="calculator">13 + 4</gadget>
<output>17</output>

<result>17</result>