If a certain project is completed by the first, second, and third teams, it will take 12 days; if it is done by the first, third, and fifth teams, it will take 7 days; if it is completed by the second, fourth, and fifth teams in 4 days; If the first, third, and fourth teams work together, it will take 42 days to complete. So how many days will it take for these five teams to work together to complete the project.
某工程如果由第一、二、三小队合干需要12天才能完成；如果由第一、三、五小队合干需要7天完成；如果由第二、四、五小队合干4天完成；如果由第一、三、四小队合干需要42天才能完成．那么这五个小队一起合干需要多少天才能完成这项工程．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/4) - (1/12)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / 42</gadget>
<output>1/42 = around 0.02381</output>

<gadget id="calculator">(1/42) - (1/12)</gadget>
<output>-5/84 = around -0.059524</output>

<gadget id="calculator">(1/7) + (1/6) + (1/4) + (-5/84)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) / 3</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/12) + (1/6)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / (1/4)</gadget>
<output>4</output>

<result>4</result>