It takes 12 days for team A to complete a project alone, and 4 days for team B to complete it alone. If team A works for a few days first, then team B will continue to do the rest of the project until it is all completed. It took 6 days together, how many days did Team A do it first?
一项工程，甲队独做需要做12天才能完成，乙队独做需要4天完成，如果甲队先做了若干天后，由乙队单独接着做余下的工程，直至全都完工，这样前后一共用去了6天，求甲队先做了几天？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/4) * 6</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">(3/2) - 1</gadget>
<output>1/2 = around 0.5</output>

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

<gadget id="calculator">(1/4) - (1/12)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/2) / (1/6)</gadget>
<output>3</output>

<result>3</result>