The easiest way to lose 3 pounds a week is to cut back on food and increase exercise, but yup, you have to manage to burn or cut back about 10,500 calories. If this is only a one week thing, you can go to an extreme, but don't continue it after one week. You probably only want to eat about 1000 calories a day, and exercise for about 3 hours a day. A good way to achieve this goal is to eat a lot of fruits, make sure to drink a lot of water, and split the exercise up. You might want to walk for an hour in the morning, play basketball for an hour and a half after lunch, and then run for about a half hour, or 3 ten minute periods at night.