A project was completed by team A alone in 12 days. Team A worked alone for 4 days, and then team B joined in. The two teams worked together to complete the task in 3 days. How many days does Team B need to practice alone?
一项工程，甲队单独做12天完成，甲队先单独做了4天，后来乙队加入，两队合修3天完成了任务．乙队单独修需要多少天？
<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(4/9) - (1/12)</gadget>
<output>13/36 = around 0.361111</output>

<gadget id="calculator">1 / (13/36)</gadget>
<output>36/13 = around 2.769231</output>

<result>36/13 = around 2.769231</result>