There is a pile of sand, and it takes 4 hours for A to transport alone, 6 hours for B to transport alone, and 8 hours for C to transport alone. After B has worked alone for 3 hours, A and C come to help at the same time, and it will take a few hours to transport the pile of sand. over?
有一堆砂，甲单独运需4小时，乙单独运需6小时，丙单独运需8小时，乙单独先工作了3小时后，甲丙同时来帮忙，还需几小时可把这堆砂运完？
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">3 * (1/6)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

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

<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">(1/4) + (1/6) + (1/8)</gadget>
<output>13/24 = around 0.541667</output>

<gadget id="calculator">(1/2) / (13/24)</gadget>
<output>12/13 = around 0.923077</output>

<result>12/13 = around 0.923077</result>