A project can be completed by team A alone in 15 days and by team B in 12 days alone. Now after the second team worked for 2 days, team A was delayed for 3 days because of something, how many days will they have to work together to complete the project?
一项工程，甲队单独做15天可以完成，乙队单独做12天可以完成．现在二队做2天后，甲队有事耽误了3天，请问他们还要合作几天才能完成这项工程？
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

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

<gadget id="calculator">(3/20) * 2</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(1/12) * 3</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (3/10) - (1/4)</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">(9/20) / (3/20)</gadget>
<output>3</output>

<result>3</result>