If A and B work together to complete a job in 3 hours, B alone can complete it in 5 hours, how many hours can A alone complete it?
一件工作甲乙合作3小时完成，乙独做5小时完成，甲独做多少小时完成．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/3) - (1/5)</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">1 / (2/15)</gadget>
<output>15/2 = around 7.5</output>

<result>15/2 = around 7.5</result>