How Can I Lose At Least 20lbs A month?

Is that reasonable? I am just over 300 pounds and i am 5'3 - Morbidly Obese :( What foods should i eat? besides just healthy foods. lol Whats healthier? And what fruits/veggies help promote weight loss? Does having more muscle burn more calories while you rest? for exercising all i have is a tony little gazelle, But im sure i could arange to go to the ymca to go swimming once or twice a week but it wont be every other day cause i don't have those options, Walking and bike riding would be nice, but i have to wait till spring to do that outside. Cause everything is icy / snowy lol And some exercises i can't do because i have extremely bad arthritis in my knees. :( I am also only 13 years old, I really want to lose weight before high school so i can look back when im older and be proud of me :) I was looking online and found something called the gabriel method, Have you tryed it? does it work? Btw : I do not want anyone posting saying i should try any diet pills, Acai berry crap or ANYTHING like that! thanks X)