Calorie refers to the amount of energy required to elevate the temperature of one gram of water through one degree Celsius. The kind of amount of food one consumes determines the number of calories consumed by the individual.
In the given case, the slice of pumpkin bread contains 5 grams of fat, 40 grams of carbohydrates, and 5 grams of protein.
One gram of fat gives 9 calories, so total calories given by fats will be 45 calories.
One gram of carbohydrate gives 4 calories, so total calories given by carbohydrates will be 160 calories.
One gram of proteins gives 4 calories, so total calories given by proteins is 20 calories.
Thus, total calories is 45+160+20 = 225,
Percent of bread's calories from fats is 45/225*100 = 20 %.