Bajie will be lazy when working alone, but he works much faster when Wukong is around, and his efficiency when working alone is only as efficient as when Wukong is around (2/5). Now there is a job that Bajie needs to complete. For the first 4 hours, Wukong watched over him. In the rest of the time, because Wukong had something to do and left, Bajie did the rest alone. As a result, he spent 12 hours together. If Bajie does all this work alone, how many hours would it take to complete it?
八戒单独干活时会偷懒，悟空在的时候干活快多了，单独干活时的效率只有悟空在时效率的(2/5)．现在有一件工作需要八戒完成，前4个小时有悟空看着，后面的时间由于悟空有事走了，剩下的工作是八戒单独做完的，结果前后共用了12小时．如果这件工作全部由八戒单独做，那么需要多少小时完成？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">12 * (2/5)</gadget>
<output>24/5 = around 4.8</output>

<gadget id="calculator">4 * (2/5)</gadget>
<output>8/5 = around 1.6</output>

<gadget id="calculator">(24/5) - (8/5)</gadget>
<output>16/5 = around 3.2</output>

<gadget id="calculator">4 + (16/5)</gadget>
<output>36/5 = around 7.2</output>

<gadget id="calculator">1 / (36/5)</gadget>
<output>5/36 = around 0.138889</output>

<gadget id="calculator">(2/5) * (5/36)</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">1 / (1/18)</gadget>
<output>18</output>

<result>18</result>