It takes 12 days for A and B to process a batch of parts. First, A works for 3 days, and then B works for 2 days. There are still (4/5) of this batch of parts that have not been completed. How many days will it take for A to finish this batch of parts by himself?
加工一批零件，甲、乙二人合作需12天完成．先由甲工作3天，然后由乙工作2天，还剩这批零件的(4/5)没完成，甲独自做完这批零件需多少天？
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</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 - (4/5) - (1/6)</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / (1/30)</gadget>
<output>30</output>

<result>30</result>