There is a project that A alone takes 12 days to complete, and C alone takes 20 days to complete. It takes 5 days for A, B, and C to cooperate. If this project is done by B alone, how many days will it take to complete it?
有一项工程，由甲单独做，需12天完成，丙单独做需20天完成．甲、乙、丙合作，需5天完成．如果这项工程由乙单独做，需多少天完成．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/5) - (1/12) - (1/20)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 / (1/15)</gadget>
<output>15</output>

<result>15</result>