Copy a book, A's work efficiency is equal to the sum of B and C's work efficiency, and C's work efficiency is equivalent to A's and B's work efficiency (1/7). If three people copy together, it only takes 12 days to complete. How many days will it take for B to copy alone?
抄一份书搞，甲的工作效率等于乙、丙两人工作效率的和，丙的工作效率相当于甲、乙工作效率的(1/7)．如果三人合抄，只需12天完成．乙单独抄，需要几天才能完成？
<gadget id="calculator">7 / 96</gadget>
<output>7/96 = around 0.072917</output>

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

<gadget id="calculator">(7/96) - (1/24)</gadget>
<output>1/32 = around 0.03125</output>

<gadget id="calculator">1 / (1/32)</gadget>
<output>32</output>

<result>32</result>