A piece of work, A, B, and C alone will take 12 hours, 18 hours, and 24 hours respectively. This work is done by A for a certain number of hours, and then B will continue to do it. The number of hours that B does is 3 times that of A. , C is the last to do it, and C takes twice as long as B to finish it. How many hours did it take?
一件工作，甲、乙、丙单独做分别要用12小时、18小时和24小时，这项工作由甲先做了若干小时，再由乙接着做，乙做的小时数是甲的3倍，最后由丙做，丙做的时间是乙的2倍，终于全部完工，共用了多少小时？
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / 18</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">(1/18) * 3</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / 24</gadget>
<output>1/24 = around 0.041667</output>

<gadget id="calculator">(1/24) * 6</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/12) + (1/6) + (1/4)</gadget>
<output>1/2 = around 0.5</output>

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

<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<gadget id="calculator">2 + 6 + 12</gadget>
<output>20</output>

<result>20</result>