A project alone takes 12 hours to complete, and A and B work together for 4 hours, and then B spends another 6 hours to complete the project. How many hours does it take B to complete it alone?
一件工程甲单独完成要12小时，甲乙合做4小时后乙又用了6小时才完成这项工程，乙单独完成要多少小时？
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/12) * 4</gadget>
<output>1/3 = around 0.333333</output>

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

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

<gadget id="calculator">(2/3) / 10</gadget>
<output>1/15 = around 0.066667</output>

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

<result>15</result>