Question 860191
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Hi,
Let x represent time  If all three presses run together-
{{{ 1/6 + 1/9 + 1/12 = 1/x }}}  |Multiplying thru by 36x so as all denominators = 1
   6x + 4x + 3x = 36
         13x = 34
           x = 34/13   0r  2 <sup>8</sup>&frasl;<sub>13</sub>