For a project, team A will complete it alone in 10 hours, team B will complete it in 15 hours alone, and team C will complete it in 20 hours alone, and the three teams will start to cooperate. Team A has another task in the middle, which will be completed by teams B and C. From the beginning to the end It took 6 hours to complete the project, how many hours did Team A actually do it?
一项工程，甲队单独做10小时完成，乙队单独做15小时完成，丙队单独做20小时完成，开始三队合作，中途甲队另有任务，由乙丙两队完成，从开始到工程完成共用了6小时，问甲队实际做了几小时？
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

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

<gadget id="calculator">(1/15) + (1/20)</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>