It takes 6 hours for A to do a job alone, and 9 hours for B to do it alone. After A finishes (1/3), how many hours will it take for both of them to work together?
一件工作，甲单独做需要6小时，乙单独做需要9小时，甲做完(1/3)后，两人合作，还要几个小时才能做完成？
<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 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">(1/6) + (1/9)</gadget>
<output>5/18 = around 0.277778</output>

<gadget id="calculator">(2/3) / (5/18)</gadget>
<output>12/5 = around 2.4</output>

<result>12/5 = around 2.4</result>