It takes 6 days for a project to be completed by teams A and B. Now Team B has been working for 7 days first, and then Team A is working for 4 days, and they have completed the project (13/15). If the rest of the project is handed over to Team B to do it alone, how many days will it take to complete it?
一项工程，甲、乙两队合做需6天完成．现在乙队先做了7天，然后甲队做了4天，共完成这项工程的(13/15)，如果把其余工程交给乙队单独做，还要几天才能完成？
<gadget id="calculator">13 / 15</gadget>
<output>13/15 = around 0.866667</output>

<gadget id="calculator">1 - (13/15)</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/6) * 4</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">(13/15) - (2/3)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) / 3</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(2/15) / (1/15)</gadget>
<output>2</output>

<result>2</result>