project. A and B cooperated in 6 days, C and D cooperated in 8 days, B and C cooperated in 7 days, how many days did A and D cooperate?
一项工程．甲、乙合作6天完成，丙、丁合作8天完成，乙、丙合作7天完成，甲、丁两队合作几天完成？
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

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

<gadget id="calculator">(1/8) - (1/7)</gadget>
<output>-1/56 = around -0.017857</output>

<gadget id="calculator">(1/6) + (-1/56)</gadget>
<output>25/168 = around 0.14881</output>

<gadget id="calculator">1 / (25/168)</gadget>
<output>168/25 = around 6.72</output>

<result>168/25 = around 6.72</result>