Hi

Tom in 12 hours...His friend Brad could paint the set in 8 hours

Let x represent time to finish the Entire set together

Per Hour KEY:

 1/12 + 1/8 = 1/x

   8x + 12x = 96

       20x = 96

         x = 4.8 hr, 

% of work w done together in 3 hr

         1/4.8 = w/3

            3 = 4.8w

            3/4.8 = .625 = w

How many more hours h will tom need to work to finish the set

 1/12 = .625/h

   h = 12(.625)= 7.5 more hours 

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