if your 80-100 lbs. u shouldn't have to worry about losing calories. Your height should be around 5 feet if your that heavy. If that's average for you than an average workout is to stretch for 30 minutes, take a light jog 2-3 times a week, and go to your local gym (at least) once a week. Maybe every other day depending on how fit you want to be. But I wouldn't worry if your only 80- 100 lbs.