For a manuscript, Li Ming typed this manuscript every hour (1/6), and Zhang Hong needed 4 hours to type this manuscript alone. If two people type this manuscript together, how many hours can it be completed?
一份稿件，李明每小时打这份稿件的(1/6)，张红单独打完这份稿件需要4小时．如果两人合打这份稿件，几小时能完成？
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

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

<gadget id="calculator">(1/6) + (1/4)</gadget>
<output>5/12 = around 0.416667</output>

<gadget id="calculator">1 / (5/12)</gadget>
<output>12/5 = around 2.4</output>

<result>12/5 = around 2.4</result>