the total kilojoules for one cup of orange juice that contains 23 g of carbohydrate, no fat, and 4 g of protein

Answer 1

If we use the averages of of cal for proteins, carbs, fats they are as follows:
proteins = 4 kcal/gram (4 grams in the problem)
carbs = 4 kcal/gram (23 grams in the problem)
fat = 9 kcal/gram (0 grams in the problem)
total kcal = 4*protein + 9*fat + 4* carb = 4*4 + 9*0 + 4*23 = 108 total kcal.
Convert to kJ. 108 kcal x 4.184 = 452 kJ