It takes 12 days for A and B to complete a project together. Now A will do it for 3 days, and then B will do it for 1 day. A total of (3/20) of this project will be completed. How many days will it take if this project is done by A alone?
甲、乙两人共同完成一项工程需要12天，现在由甲做3天后，再由乙接着做1天，共完成这项工程的(3/20)．如果这项工程由甲独做需要多少天．
<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">3 - 1</gadget>
<output>2</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>