For a manuscript, typist A can finish typing in 6 hours alone, and typist B can finish typing in 4 hours alone. If two people work together, how many hours can they finish typing?
一篇稿件，甲打字员独打6小时完成，乙打字员独打4小时可打完这篇稿件的，两人合打，几小时可以打完这篇稿件的？
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">3 / 12</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/12) + (1/4)</gadget>
<output>1/3 = around 0.333333</output>

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

<result>3</result>