The two masters and apprentices cooperate to complete a batch of parts, which can be completed in 12 days. The master does it for 4 days first, and the apprentice does it for 2 days, and the task is completed (1/4). If the master does it alone, how many days can the task be completed?
师徒二人合作一批零件，12天可以完成，师傅先做4天，徒弟接着做了2天，共完成任务的(1/4)．如果师傅单独做，多少天可以完成任务？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">(1/12) * 2</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/4) - (1/6)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">(1/12) / 2</gadget>
<output>1/24 = around 0.041667</output>

<gadget id="calculator">1 / (1/24)</gadget>
<output>24</output>

<result>24</result>