It will take 12 days for A and B to manufacture a batch of parts. Now A has made it for 3 days and B will make it for 1 day. A total of (3/20) of this batch of parts will be completed. If A alone does it, how many days will it take to finish it?
甲乙两人共同制造一批零件要12天完成，现由甲制造了3天后再由乙做1天，共完成这批零件的(3/20)．如果由甲独做，需要几天做完？
<gadget id="calculator">3 / 20</gadget>
<output>3/20 = around 0.15</output>

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

<gadget id="calculator">(3/20) - (1/12)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/15) / 2</gadget>
<output>1/30 = around 0.033333</output>

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

<result>30</result>