If the municipal government renovates a certain project, if the construction is carried out alone, engineering team A can complete it 4 days earlier than the specified date, and engineering team B can complete it 6 days later than the specified date. If the two engineering teams A and B cooperate 4 days later, the remaining If the work is completed by B engineering team alone, it will be completed on the specified date. How many days will it take for teams A and B to cooperate to complete this project?
市政府改造某个项目，若单独施工，甲工程队可以比规定日期提前4天完成，乙工程队则要超过规定日期6天才能完成，如果现由甲乙两个工程队合作4天后，剩余的工作由乙工程队单独完成，那么刚好在规定日期完成．求甲乙两队合作完成此项工程需要多少天？
<gadget id="calculator">4 + 6</gadget>
<output>10</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 - (2/3)</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">10 / (1/3)</gadget>
<output>30</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">30 - 10</gadget>
<output>20</output>

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

<gadget id="calculator">(1/30) + (1/20)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / (1/12)</gadget>
<output>12</output>

<result>12</result>