First, in my opinion, losing 3lbs per week is not healthy - regardless of what you see on tv shows like Biggest Loser, etc. A healthy and attainable goal that you can do over the long-term is 0.5 to 1.5lbs per week. This is realistic and will also help you avoid any health issues or lose skin.
The caloric intake varies on many different variables but with the information you have given and with exercise three days per week you would be looking at roughly 2000-2300 calories per day.