losing 10 pounds in 3 weeks is not really a good idea. i heard that u shouldn't lose more than 2 pounds a week. if u lose more than that, that means u r also losing muscle which helps u to burn more calories throughout the day. u should eat properly breakfast. for lunch and dinner, eat whatever your family eats but a bit less. for snack, eat a piece of fruit or veggie. if u miss eating ur fav junk food, then just eat it once or twice a week so u r not depriving urself from any food. as for exercise, 30 minutes of aerobic exercise for 4 to 5 times is enough. if u can do 45 minutes, that's better but don't overdo it. u should also lift weight to develop muscle. hope i helped! bye