A project is completed in 18 days by A alone, 15 days by B alone, A and B work together, but A asks for leave for 4 days in the middle, so how many days did A actually complete the task?
一项工程，甲独做18天完成，乙独做15天完成，甲、乙两人合做，但甲中途有事请假4天，那么甲完成任务时实际做了多少天？
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/15) * 4</gadget>
<output>4/15 = around 0.266667</output>

<gadget id="calculator">1 - (4/15)</gadget>
<output>11/15 = around 0.733333</output>

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

<gadget id="calculator">(1/18) + (1/15)</gadget>
<output>11/90 = around 0.122222</output>

<gadget id="calculator">(11/15) / (11/90)</gadget>
<output>6</output>

<result>6</result>