It takes 12 days for A to complete a job alone, and 15 days for B to complete it alone. After two days of cooperation, A leaves for something, and B will do the rest alone. How many days will B have to work to complete?
一项工作甲独做需12天完成，乙独做要15天完成，两个合作2天后，甲有事离去，剩下的由乙独作，乙还要工作几天才能完成？
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/12) + (1/15)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(3/20) * 2</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (3/10)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">(7/10) / (1/15)</gadget>
<output>21/2 = around 10.5</output>

<result>21/2 = around 10.5</result>