Two engineering teams work together to lay a pipeline. It takes 15 days for team A to lay it alone, and 20 days for team B to lay it alone. sky?
两个工程队合作铺设一条管道，甲队单独铺设要做15天，乙队单独铺设要做20天，甲乙两队合作6天后，乙队因接其它工程，剩下的由甲单独完成需要多少天？
<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">(3/10) / (1/15)</gadget>
<output>9/2 = around 4.5</output>

<result>9/2 = around 4.5</result>