I am a 17 years old boarding boy wishing to loose fat on belly and thigh and hip in 3 weeks and i am wonder what would be the most effective and fast.

Diet: You do not say how much weight you want to lose. If you cut out sugar, junk food and most other carbohydrates (breads, rice, pasta) and stick to protein and veg, the weight will come off. Fruit, and milk products, are ok, but not a lot. If you want to know your ideal weight, see your doctor. Once you reach it, you can add carbs back in. Also, 30 minutes of daily exercise helps burn calories.