A job, A and B work together to complete it in 9 days, A has done (2/5) when it is completed, how many days does it take for B to do it alone?
一项工作，甲乙合干9天完成，完成时甲干了(2/5)，求乙独干这工作几天完成？
<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) / 9</gadget>
<output>2/45 = around 0.044444</output>

<gadget id="calculator">(1/9) - (2/45)</gadget>
<output>1/15 = around 0.066667</output>

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

<result>15</result>