Of course, forgot about the OP -
m = d
M D
m is how much to add
m is the weight of the aircraft
d is the change in C of G (7% or .245 m)
D is the change in distance (.805 m).
m = .245 x 47800 = 14547 kg or 20205 ltrs or 4535 Imp gals
.805
tabbing may be a bit off