Afood contains 28g carbohydrates, 2.7g protein, and 0.3g fats. how many calories does that food provide?

A carbohydrate will provide 4 kcal/g, protein also 4kcal/g, but fat is 9 kcal/g. In this case, there are 28g carbohydrates, 2.7g protein, and 0.3g fat. Counting it separately, it will be:
Carbohydrate: 28g * 4kcal/g  = 112kcal
Protein            : 2.7g * 4kcal/g =   10,8 kcal
Fat                  : 0.3 * 9kcal/g   =     2.7 kcal
Total calorie= 112+10.8+2.7= 125.5 kcal

Hope help!