It's not doable if you want to keep it off and would be extremely damaging to your health. In general, women should not eat less than 1200 calories a day or your body will go into "starvation mode" and make it even harder for the weight to be lost and impossible to get the nutrients your body needs. Generally one should only lose 1-2 pounds a week and the less you weigh, the harder that is.

Check out http://www.caloriesperhour.com and their tutorial.