A project can be completed in 6 hours by A alone, and 4 hours by B alone. Now A does (1/3) first and then the two cooperate. How many hours will it take to complete?
一件工程，甲独做6小时完成，乙独做4小时完成，现甲先做(1/3)后，两人再合作，还需几小时完成？
<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 / 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>