project can be completed by team A alone in 15 days and by team B in 12 days alone. Now Team A will do the work for 6 days first, and the rest will be done by the two teams. How many days will it take to complete the project?
一项工程，甲队单独做15天完成，乙队单独做12天完成．现在由甲队先做6天，剩下的由两队合作，还要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">6 * (1/15)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</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">(3/5) / (3/20)</gadget>
<output>4</output>

<result>4</result>