job alone takes 12 days, and B alone takes 8 days. Now how many days will it take for A to do the rest after working together for 4 days?
一项工作，甲单独做要12天，乙单独做要8天，现二人合作4天后，余下的由甲单独做，还要多少天．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">(1/12) + (1/8)</gadget>
<output>5/24 = around 0.208333</output>

<gadget id="calculator">(5/24) * 4</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">1 - (5/6)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/6) / (1/12)</gadget>
<output>2</output>

<result>2</result>