A project can be completed in 18 days or B in 15 days. If two people work together, and A takes a break for 4 days in the middle, how many days will it take from start to finish?
甲18天或乙15天可以完成一项工程．如果两人合作，中途甲休息4天，自开始到完工共需多少天．
<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>