job can be completed in 18 days by A alone, and the time spent by B alone is A's (5/6). After B worked for a period of time, A and B worked together again. It took 6 days to complete the remaining tasks. How many days did B work alone?
一项工作，甲独做18天完成，乙独做用的时间是甲的(5/6)．乙先工作一段时间后，甲再和乙一起工作，完成剩下任务用了6天，乙单独工作了多少天．
<gadget id="calculator">1 / 18</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">5 / 6</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">18 * (5/6)</gadget>
<output>15</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

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

<gadget id="calculator">(11/90) * 6</gadget>
<output>11/15 = around 0.733333</output>

<gadget id="calculator">1 - (11/15)</gadget>
<output>4/15 = around 0.266667</output>

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

<result>4</result>