Two teams, A and B, plant trees in land A and B respectively. The number of trees planted in land B is twice that of land A. It is known that team A needs 12 days to plant trees in land A alone, and team B needs to plant trees in land B alone. 30 days to complete. Now teams A and B start at the same time in places A and B respectively, and when team A finishes, they go to place B to work together with team B. May I ask: How many days will it take for the two teams to plant the tree?
甲、乙两队分别在A、B两块地植树，B地需要植树的数量是A地的两倍，已知甲队单独在A地植树需要12天完成，乙队单独在B地植树需要30天完成．现在甲、乙两队分别在A、B两地同时开始，当甲队做完后便去B地和乙队共同工作．请问：两队要用多少天才能种完树？
<gadget id="calculator">2 / 30</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/15) * 12</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">2 - (4/5)</gadget>
<output>6/5 = around 1.2</output>

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

<gadget id="calculator">(1/12) + (1/15)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(6/5) / (3/20)</gadget>
<output>8</output>

<result>8</result>