There is a road that needs 20 days for team A to repair alone, 30 days for team B to repair alone, and 40 days for team C to repair alone. Now let the three teams jointly repair it, but team A in the middle withdraws to another construction site, and it ends up being used. It took 12 days to complete the repair of this road. May I ask: After Team A withdrew, how many days did it take for Team B and C to complete the joint cultivation together?
有一条公路，甲队单独修需20天，乙队单独修需30天，丙队单独修需40天，现在让三个队合修，但中间甲队撤出去到另外工地，结果用了12天才把这条公路修完．请问：当甲队撤出后，乙、丙两队又共同合修了多少天才完成？
<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

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

<gadget id="calculator">(1/30) + (1/40)</gadget>
<output>7/120 = around 0.058333</output>

<gadget id="calculator">(7/120) * 12</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 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(3/10) / (1/20)</gadget>
<output>6</output>

<gadget id="calculator">12 - 6</gadget>
<output>6</output>

<result>6</result>