Three trucks, A, B, and C, want to transport two piles of goods A and B with the same quantity. If A pile of goods is transported separately, it takes 9 hours for truck A, 12 hours for truck B, and 18 hours for truck C. At the beginning, A helps B to transport pile A, and C alone transports pile B. After a period of time, A turns to pile B to help C carry until finally, the two piles of goods are shipped out at the same time. How long will A and C be transported?
甲、乙、丙三辆卡车要运送A、B两堆数量相同的货物，若单独运A堆货物，甲车需9时，乙车需12时，丙车需18时．开始时，甲帮乙运A堆，丙单独运B堆，一段时间后，甲又转向B堆帮丙运直至最后，两堆货物被同时运完．甲帮丙运了几时？
<gadget id="calculator">1 / 18</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/9) + (1/12) + (1/18)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">2 / (1/4)</gadget>
<output>8</output>

<gadget id="calculator">(1/18) * 8</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">1 - (4/9)</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">(5/9) / (1/9)</gadget>
<output>5</output>

<result>5</result>