A project can be completed by A in 18 days and by B in 15 days. Two people work together, and A takes a rest for 4 days due to illness, how many days does it take from start to finish?
一项工程，甲独做18天完成，乙独做15天完成．两人合做，甲因病休息了4天，自开工到完工共用多少天？
<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>

<gadget id="calculator">6 + 4</gadget>
<output>10</output>

<result>10</result>