How to add M1,M2,M3, etc - (May/05/2017 )

In my experiment with deuterated water labeling, peaks for M1,M2 M3 etc represent the deuterium-labeled fractions of my samples. What formula would I use to add these peaks? I have data for the labeled samples as well as unlabeled controls, which represent normal heavy water background. Thank you. 

I think, but I would check this before using (as I don't really know), that you would take the area under the peak and then simply sum the areas.