If you are a 5' 8 145 pound 15-year-old how many calories per day should you eat to lose 20 pounds?

I'm also 5'8'' and 145. I'm in school for exercise physiology actually and there is no way you should be trying to loose 20 lbs. I just try to simply eat plenty of large salads, soups, and rarely ever have desert. If you eat well and work out (i do about 4 days at the gym) each week you'll be simply muscle mass and look just great and toned. Everyone will think that you look just as thin as if you lost the weight.