certain park needs to pave walkways. Team A can complete the pavement in 20 days alone, and team B can complete the work in 9 days (3/4). If the two teams cooperate, how many days can it be completed?
某公园需要铺步行道，甲队单独铺20天可以完成，乙队单独铺9天可以完成这项工作的(3/4)，如果两队合作，多少天可以完成？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">(3/4) / 9</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/20) + (1/12)</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">1 / (2/15)</gadget>
<output>15/2 = around 7.5</output>

<result>15/2 = around 7.5</result>