how do u lose weight fast lyk ne tricks how long wil it take 2 lose lyk 3 kgs

and what is a gud weight 4 15-16 yrs at 5.6 foot?

i dnt drink da much coke ect mstly water and am outside 4 lyk 1.5 hrs in winta nd 3 hrs in sumer + walting round at skul 1/2 hr