It takes 12 days for team A to complete a project alone, and 15 days for team B to complete it alone. After 4 days of cooperation between the two teams, only one team will be left to complete the rest of the project. How many days will it take at least?
一项工程，甲队单独做需要12天完成，乙队单独做需要15天完成，两队合作4天后，只留下一个队完成剩下的工程，最少还需多少天？
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</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">(3/20) * 4</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) / (1/12)</gadget>
<output>24/5 = around 4.8</output>

<result>24/5 = around 4.8</result>