Project A can be completed by team A in 20 days and team B in 30 days. Project B can be completed by team A in 45 days and team B in 30 days. How many days will it take for the two teams to work together to complete Project A and Project B?
A工程，甲队独做20天完成，乙队独做30天完成．B工程，甲队独做45天完成，乙队独做30天完成．现在由两队合作完成A、B工程几天完成？
<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">1 / (1/12)</gadget>
<output>12</output>

<gadget id="calculator">1 / 45</gadget>
<output>1/45 = around 0.022222</output>

<gadget id="calculator">(1/45) + (1/30)</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">1 / (1/18)</gadget>
<output>18</output>

<gadget id="calculator">12 + 18</gadget>
<output>30</output>

<result>30</result>