Question 883606
Keep going!   You have descriptions for two rates and almost have them in number symbolism.  


Man & Wife, {{{1/12}}} keg/day
Man alone,  {{{1/20}}} keg/day


The sum of their individual rates is the Man-plus-Wife combined rate.  You just do not yet know the wife's rate.  


Let w = rate of drinking for the wife alone, keg/day.
{{{highlight(1/20+w=1/12)}}}.
Solve for w.
Note that w will be a fraction.  Taking the inverse of w will then be the DAYS per 1 KEG drink rate for the wife.