To welcome the 2008 Olympic Games and complete a project, Team A will complete it in 20 days alone, and Team B will complete it in 30 days alone. Team A completed (1/4) of the project first, and then team B joined in the construction. How many days did the two teams cooperate to complete the project?
迎2008年奥运，完成一项工程，甲队单独做20天完成，乙队单独做要30天完成．甲队先干了这项工程的(1/4)后，乙队又加入施工，两队合作了多少天完成这项工程？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

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

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/20) + (1/30)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(3/4) / (1/12)</gadget>
<output>9</output>

<result>9</result>