Devi Singh is an efficiency expert working for a major industrial firm. She determines that the daily output of a worker who has been on the job for t weeks is given by a function of the form Q(t) = 40 − Ae^−kt. Devi observes that a typical worker produces 20 units a day initially and after 1 week, produces 30 units a day. How many units per day should Devi expect a typical worker to produce after 3 weeks?