Not much, what's up with you?
Do you have fewer muscles in your body than the rest of us, or did you mean 20 pounds?
Good so far...
Doh!! You had me at "add muscle mass". You want to gain weight to lose weight?! If your friends at school jump off a bridge are you...never mind.
You could, if done properly,
Seriously though. Proper diet andgood exercise will transfer a body quickly, especially if my assumption that you're young and inexperienced. Read up on this site for good training and diet tips.
How are your friends eating that causes you such jealousy? You need to eat for success, make them wish they could eat like you and look like you do when you transform your body. Or just give up and have another McNugget.