To calculate the total number of calories in a serving of crackers, we need to multiply the number of grams of each macronutrient (fat, carbohydrate, and protein) by the number of calories per gram for that macronutrient, and then add up the results.
The number of calories per gram for each macronutrient is:
- Fat: 9 calories per gram
- Carbohydrate: 4 calories per gram
- Protein: 4 calories per gram
Using these values, we can calculate the total number of calories in a serving of crackers as follows:
Total calories = (4 grams of fat x 9 calories per gram) + (21 grams of carbohydrate x 4 calories per gram) + (2 grams of protein x 4 calories per gram)
Total calories = 36 + 84 + 8
Total calories = 128
Therefore, there are 128 total calories available from a serving of crackers that contains 4 grams of fat, 21 grams of carbohydrate, and 2 grams of protein.