It takes 60 days for team A to dig a tunnel alone, and 40 days for team B to do it alone. The two teams chiseled from both sides at the same time. When the two teams were still (1/6) away from the entire hole length, how many days had they been working?
开凿一条隧道，甲队单独干要60天完成，乙队单独干要40天完成．两队同时从两侧对凿，当两队还距整个洞长的(1/6)时，已工作了多少天？
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 - (1/6)</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">1 / 60</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">1 / 40</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">(1/60) + (1/40)</gadget>
<output>1/24 = around 0.041667</output>

<gadget id="calculator">(5/6) / (1/24)</gadget>
<output>20</output>

<result>20</result>