I read this question quite diferently as he asked for the STN position of the new CG if 2500KG were to be added to the Aircraft in the cargo hold @ STN 360.
Wether or not it is within the % mac range is irrelevent to the question as he ONLY asked for the new position to be calculated which as Keith has done is 649.59. End of story I thought but then I am certainly not always right...