A project can be completed by A alone in 15 days and by B in 12 days. After the two teams work together for a few days, the rest will be completed by B alone in 3 days. How many days did A and B work together?
一项工程，甲独做15天完成，乙独做12天完成．现两队合做若干天后，剩下的由乙独做3天才完成．甲、乙合做了多少天．
<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">(1/15) + (1/12)</gadget>
<output>3/20 = around 0.15</output>

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

<result>5</result>