A calorie is a unit of energy and can be explain as energy consumption and energy usage trough phisical activity.
1 gr of carbs = 4 calories
1 gr of protein = 4 calorie
1 gr of fat = 9 calories
1 gr of sugar =4 calories
Have a look at the nutritional label of the product and do the following
(Number of carbs x 4) +(numbers of protein X 4)+ (numbers of fat X 9) so on to complete your equation then solve .
Is also good to know that anything under a gram won’t be mentioned on the nutritional label and will show a 0 value but that doesn’t mean no calories at all . So your food may contain extra calories