To complete a job, A alone can finish it 3 days earlier than the specified time, while B alone can complete it 5 days longer than the specified time. If A and B cooperate for 3 days first, B will continue to do the rest of the work alone. Then it happens to be completed within the specified time, how many days will it take for A and B to cooperate?
完成一项工作，甲独做可比规定时间提前3天完成，乙独做则要超过规定时间5天才能完成，如果甲、乙两人先合作3天，剩下的工作继续由乙单独做，那么刚好在规定时间内完成，求甲、乙两人合作要多少天完成？
<gadget id="calculator">3 * 5</gadget>
<output>15</output>

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<gadget id="calculator">15 + 15</gadget>
<output>30</output>

<gadget id="calculator">5 - 3</gadget>
<output>2</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">15 - 3</gadget>
<output>12</output>

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

<gadget id="calculator">15 + 5</gadget>
<output>20</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/12) + (1/20)</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">1 / (2/15)</gadget>
<output>15/2 = around 7.5</output>

<result>15/2 = around 7.5</result>