To complete a project, team A alone needs 10 days, team B needs 15 days, and team C needs 20 days. At the beginning, three teams worked together, but team A withdrew midway due to work needs. As a result, it took a total of 6 days to complete the project. Q: How many days did Team A actually work?
完成某项工程，甲队独做需要10天，乙队独做需要15天，丙队独做需要20天．开始三个队一起干，因工作需要甲队中途撤走了，结果一共用了6天完成这一工程．问：甲队实际工作了几天？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

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

<gadget id="calculator">(1/20) + (1/15)</gadget>
<output>7/60 = around 0.116667</output>

<gadget id="calculator">(7/60) * 6</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">1 - (7/10)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

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

<result>3</result>