For a project, it takes 12 days for team A to do it alone, and 15 days for team B to do it alone. After the two teams work together for a few days, team B is transferred for 3 days to support other projects, and then completes the whole project together with team A , How many days did the two teams cooperate in total?
一项工程，甲队独做需要12天，乙队独做需要15天，两队合做若干天后，乙队因支援其它工程，调走了3天，然后又与甲队一起将全部工程完成，两队一共合作了多少天．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/12) * 3</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

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

<gadget id="calculator">(3/4) / (3/20)</gadget>
<output>5</output>

<result>5</result>