A job can be completed by A doing it for 6 hours first, and then B can do it for 12 hours. If A does it for 8 hours first, and B can do it for another 6 hours, how many hours will it take for B to do it alone?
一件工作甲先做6小时，乙接着做12小时可以完成，如果甲先做8小时，乙接着做6小时也可以完成，如乙独做需多少小时完成？
<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<gadget id="calculator">18 + 12</gadget>
<output>30</output>

<result>30</result>