project can be completed in 12 hours by A alone, 15 hours by B alone, and 18 hours by C alone. If A works for 1 hour first, then B takes over from A for 1 hour, and then C takes over from B Work for 1 hour, and then A will replace C for 1 hour...Three people work alternately in this way, how many hours did it take to complete the project?
一件工程，甲独做要12小时完成，乙独做要15小时完成，丙独做要18小时完成，如果先由甲工作1小时，然后由乙接替甲工作1小时，再由丙接替乙工作1小时，再由甲接替丙工作1小时…三人如此交替工作，那么完成这工程时共用了多少小时？
<gadget id="calculator">3 * 4</gadget>
<output>12</output>

<gadget id="calculator">64 / 360</gadget>
<output>8/45 = around 0.177778</output>

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

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/12) + (1/15)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(8/45) - (3/20)</gadget>
<output>1/36 = around 0.027778</output>

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

<gadget id="calculator">(1/36) / (1/18)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">12 + 2 + (1/2)</gadget>
<output>29/2 = around 14.5</output>

<result>29/2 = around 14.5</result>