Final answer:
To lose a pound of fat, you need to expend an extra 3,500 calories.
Step-by-step explanation:
To lose a pound of fat, you need to expend an extra 3,500 calories than you ingest. This means that option 3) 3500 is the correct answer. When your body uses more calories than it consumes, it begins to metabolize body fat. Remember that the number of calories needed varies depending on factors such as body mass, age, height, gender, and activity level.