If it takes Master Wang 6 hours to complete a project alone and Master Li 4 hours to complete it alone, how many hours will it take for the two to work together?
一项工程，王师傅单独做需要6小时完成，李师傅单独做需要4小时完成，那么两个人合作需要多少小时完成．
<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>