There are two ways to figure this out. First you can look at the total weight of the package, calculate the total calories in the package (sounds like 100 calories), and then divide those 100 calories by how many grams or ounces are in the package. Now you know how many calories per gram or ounce there are in the stuff. Next measure out your tablespoon and weigh it. Multiply the number of grams/ozs your scoop is by the number of calories that are in an oz or gram. There is your answer.
If you don't have a scale you might have to get a bit messy. Get two bowls and pour a whole package of the stuff into a bowl. Using your tablespoon, transfer all the powder from one bowl to the other counting how many spoons you used. Divide the total number of calories in the pack (100) by that number. There is your answer. So, for example, if you found the pack contained five tablespoons of powder, you would divide 100 by 5 and get 20, meaning every tablespoon had 20 grams.
Sure they are both a hassle but if you eat it every day it is worth knowing?