For a project, team A works for 4 days first, and after completing (1/5) of the project, team B joins in and works together, and it takes another 6 days to complete the entire project. How many days does it take for team B to do this project alone?
一项工程，甲队先做4天，完成工程的(1/5)后，乙队也参加一起做，又做6天才完成全部工程，求乙队单独做这项工程需要多少天？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) / 4</gadget>
<output>1/20 = around 0.05</output>

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

<gadget id="calculator">(1/20) * 10</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) / 6</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / (1/12)</gadget>
<output>12</output>

<result>12</result>