A job alone takes 6 hours and B alone takes 4 hours. After A completes (1/3) of all the work, how many hours will it take for the two to cooperate.
一件工作，甲单独做要用6小时，乙单独做要用4小时．甲做完全部工作的(1/3)后，两人合作，还要多少小时才能做完．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (1/3)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/6) + (1/4)</gadget>
<output>5/12 = around 0.416667</output>

<gadget id="calculator">(2/3) / (5/12)</gadget>
<output>8/5 = around 1.6</output>

<result>8/5 = around 1.6</result>