To process a batch of parts, A alone can complete it in 12 days, B alone can complete it in 18 days, and A and B can jointly process it in 4 days. How many days will it take for A to complete the rest alone?
加工一批零件，甲独做12天完成，乙独做18天完成，甲、乙两地先合做了4天，剩下的甲单独做需要多少天可以完成？
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / 18</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">(1/12) + (1/18)</gadget>
<output>5/36 = around 0.138889</output>

<gadget id="calculator">(5/36) * 4</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">1 - (5/9)</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">(4/9) / (1/12)</gadget>
<output>16/3 = around 5.333333</output>

<result>16/3 = around 5.333333</result>