How many pounds can i lose in two months?

i'm 141 pounds. 15 year old girl. 5 feet. im already a member of a gym and have started exercising the past week...i'm doing. 3 days of 1 hour cardio (30 minutes treadmill 30 minutes elliptical) i generally lose 480 pounds on that day. 3 days 30 minute cardio (lose 200 calories) w/ strength training.. then one day of something just random..treadmill, yoga, kickboxing, whatever. i do scattered runs and i walk 30 minutes everyday. my diet is my weakness...thanks to the jugo juice right in my sports club. but i don't eat junk food and i'm trying to cut down excess sugar and fat.. i love trail mix w/ almonds, cranberries, walnuts, pecans, etc. tea..milk..salmon..i know how to eat healthy and i'll take it there. i'm aware i need to lose 3500 calories to lose a pound...and i'm looking about in the first 2/3 weeks i can lose 2/3 pounds each week...but it'll obviously get harder and there will be weaks i'll just lose 1 pound...i just want to know if it's in anyway possible for me to lose 20 pounds in 2 months in a healthy way. i am willing to exercise 2 hours a day if i have to but i will not cut down meals and such..i still am a growing teenager after all (:. thanks so much and please answer!