It takes 15 hours to type a 6,000-word manuscript for Xiao Ming alone, and 12 hours for Xiao Gang. If two people type together, how many hours can the manuscript be completed?
打一份文稿6000字，单独打小明要15小时，小刚要12小时，如果两人合打，几小时后可以完成这份文稿？
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

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

<gadget id="calculator">1 / (3/20)</gadget>
<output>20/3 = around 6.666667</output>

<result>20/3 = around 6.666667</result>