For a project, team A works for 4 days first, and after completing (2/5) of the project, team B also joins in. It takes a total of 6 days to complete the project. If team B does this project alone, how many days will it take Finish?
一项工程，甲队先做4天，完成了工程的(2/5)后，乙队也参加进来，共做了6天才完成这项工程，若乙队单独做这项工程，需要多少天完成？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) / 4</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) * 6</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) / 2</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / (1/5)</gadget>
<output>5</output>

<result>5</result>