mass added ÷ old total mass =
change of CG ÷ distance from hold to new CG
or
mass added ÷ new total mass = change of CG ÷ distance from hold to old
CG
..and you use the version that fits the data. Here we
have the distance from the hold to the old CG so we must use the new
total mass:
mass added ÷ new total mass = change of CG ÷ distance from hold to old CG
change of CG = (mass added ÷ new total mass) x distance from hold to old CG
= (450 ÷ 2400) x 1.75 = 0.328m