A job can be completed in 4 hours by the cooperation of A, B, and C. If A works for 4 hours, B and C cooperate for 2 hours, and C works for another 2 hours, the job can be completed (11/18), How many hours will it take for A and C to complete this work together?
一项工作，甲、乙、丙三人合作，4小时可以完成，如果甲做4小时，乙、丙合作2小时后，丙再做2小时，可以完成这项工作的(11/18)，这项工作由甲、丙合作需几小时完成？
<gadget id="calculator">11 / 18</gadget>
<output>11/18 = around 0.611111</output>

<gadget id="calculator">1 - (11/18)</gadget>
<output>7/18 = around 0.388889</output>

<gadget id="calculator">(7/18) * 2</gadget>
<output>7/9 = around 0.777778</output>

<gadget id="calculator">1 - (7/9)</gadget>
<output>2/9 = around 0.222222</output>

<gadget id="calculator">(2/9) / 4</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">1 / (1/18)</gadget>
<output>18</output>

<result>18</result>