To do a project, A needs 6 days to complete, and B needs 12 days to complete. In fact, this project is done by A first, and then B will complete the project, and the working hours of A and B are equal. How many days will it actually take to complete this project?
做一项工程，甲需要6天完成，乙需要12天完成，实际上，这项工程是由甲先做，然后乙接着完成，而且甲与乙的工作时间相等．请问实际完成这项工程的时间是多少天．
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

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

<gadget id="calculator">(1/6) + (1/12)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / (1/4)</gadget>
<output>4</output>

<gadget id="calculator">4 + 4</gadget>
<output>8</output>

<result>8</result>