A project can be completed in 15 hours by A alone, and 12 hours by cooperation of A and B, how many hours will it take for B to do it alone?
一项工程，甲单独做15小时完成，甲乙合作12小时完成，乙单独做需要多少小时．
<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>1/60 = around 0.016667</output>

<gadget id="calculator">1 / (1/60)</gadget>
<output>60</output>

<result>60</result>