A project can be completed by A in 10 hours alone, and B in 15 hours by himself. Now A works in 2 hours first and B continues. How many hours will it take to complete?
一项工程，甲单独做10小时完成，乙独做15小时完成，现由甲先做2小时后，乙接着做，还需多少小时完成？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) * 2</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

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

<gadget id="calculator">(4/5) / (1/15)</gadget>
<output>12</output>

<result>12</result>