If I understand this correctly......
Not counting lunch, it takes Brent 7 hrs to do the job alone and Garth 5 hrs to do the job alone
Working together they completete (1/7 + 1/5) = 12 / 35 of the job each hour
So.......they will take 35 / 12 hrs to do the job working together ≈ 2.916 hrs
So .916 * 60 ≈ 55 min
So.....working together.......they would finish the job at ≈ [ 9 + 2 ] hrs + [ 55 min ] ≈
11 : 55 AM [ with no lunch ]
12: 55 PM [ if they take a lunch break any time before 11 : 55 AM ]