Question 389585
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Hi
Let x represent the time together
Questions States***  Per hour being the equalizer...
 1/6 + 1/9 = 1/x  Multiplying each term by 36x so as all denominators = 1
  6x + 4x = 36
     10x = 36 
       x = 3.6hrs

CHECKING our Answer***
 6/36 + 4/36 = 10/36 =  1/ 36/10