There are two projects A and B. A needs 9 days to do A project, and 12 days to do B project; B needs 3 days to do A project, and 15 days to do B project. What is the minimum number of days for two people to work together on these two projects?
有A、B两项工程，甲做A工程需9天，做B工程需12天；乙做A工程需3天，做B工程需15天．两人合作这两项工程最少需多少天？
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/12) * 3</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 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/12) + (1/15)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(3/4) / (3/20)</gadget>
<output>5</output>

<gadget id="calculator">3 + 5</gadget>
<output>8</output>

<result>8</result>