For ' H ' hours of work . . .
Flourish . . . Cost = 120H
Green Thumb . . . Cost = 70H + 16,000
Their costs are the same when 120H = 70H + 16,000
Subtract 70H from each side: 50H = 16,000
Divide each side by 50 : H = 320 Hours
-- For less than 320 hours, Flourish costs less than Green Thumb.
-- For exactly 320 hours, they both cost the same.
-- For more than 320 hours, Green Thumb costs less than Flourish.