I believe you have to multiply the bow paddler's weight by that paddler's distance from the COG of the boat. Then you divide the result by the stern paddler's weight. This result will give you the distance of the stern paddler from the COG.
Example: bow paddler at 115 lbs located at 36" ahead of the COG equals 4,176. This result (4,176) divided by the stern paddler's 200 lbs equals 20.88" behind the COG. Of course you have to measure from the same location on the paddler's two bodies. Either both from their back, both from their stomach or both from their actual center of balance. This would position the kayak in the proper trim.

Glen in Baie-St-Paul.