A job can be completed by A for 6 hours and then by B for 12 hours. If B does it for 6 hours first, then A can do it for 8 hours. Then A will do it for 2 hours first, and then how many hours will it take for B to do it again.
一件工作先由甲做6小时，再由乙接着做12小时可以完成．如果先由乙做6小时，再由甲接着做8小时也可以完成．那么甲先做2小时，再由乙做还需多少小时．
<gadget id="calculator">12 - 6</gadget>
<output>6</output>

<gadget id="calculator">8 - 6</gadget>
<output>2</output>

<gadget id="calculator">6 - 2</gadget>
<output>4</output>

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<gadget id="calculator">12 + 12</gadget>
<output>24</output>

<result>24</result>