A project needs 18 days to be completed by one, two, and three teams, 15 days to be completed by two, three, and four teams, and 12 days to be completed by one, two, and four teams. , The four teams work together to complete in 20 days. How many days will it take for the first team to do it alone?
一项工程，由一、二、三小队合干需18天完成，有二、三、四小队合干需15天完成，由一、二、四小队合干需12天完成，由一、三、四小队合干需20天完成．由第一小队单独干需要多少天完成？
<gadget id="calculator">1 / 18</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</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">(1/18) + (1/15) + (1/12) + (1/20)</gadget>
<output>23/90 = around 0.255556</output>

<gadget id="calculator">(23/90) / 3</gadget>
<output>23/270 = around 0.085185</output>

<gadget id="calculator">(23/270) - (1/15)</gadget>
<output>1/54 = around 0.018519</output>

<gadget id="calculator">1 / (1/54)</gadget>
<output>54</output>

<result>54</result>