To lose weight, Dahlia needs to create a calorie deficit, which means she burns more calories than she consumes. The amount of calories she burns each day is the sum of her basal metabolic rate (BMR), which is the energy needed to maintain her body functions, and her physical activity level (PAL), which is the energy needed for her exercise and daily activities. The amount of calories she consumes each day is her energy intake from food and beverages.
To lose one pound of body fat, Dahlia needs to create a calorie deficit of about 3500 calories, since one pound of fat contains about 3500 calories of energy. To lose 5 pounds, she needs to create a calorie deficit of 5 x 3500 = 17500 calories.
If Dahlia expends an extra 300 kcals exercising each day and reduces her energy intake by 200 kcals/day, she creates a daily calorie deficit of 300 + 200 = 500 kcals. To create a total calorie deficit of 17500 kcals, she needs to maintain this daily calorie deficit for 17500 / 500 = 35 days.
Since there are 7 days in a week, it will take her 35 / 7 = 5 weeks to lose 5 pounds.