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To answer this question we will use the formula:
change of mass / new total mass = change of CG / distance from mass to old CG
re-arranged we get:
distance from mass to old CG = (new total mass x change of CG) / change of mass
= (250000 kg x +2 m) / 10000 kg
= 50 m.
By convention, arms aft of the datum are positive and arms forward of the datum are negative.
The CG moved aft (or in the +ve direction) when the mass was added, so this tells us that the mass must have been added aft of the original CG, or put another way, the original CG is forward (or in the -ve direction) of the mass that was added.
From the arm of where the mass was added (+24) we must move forward (-ve) 50 m, so the original CG must have been -26 m, or 26 meters forward of the datum.