Mass x arm = moment
Original mass 460000N x 15.4m = 7084000Nm
Add mass 12000N x 10m = 120000Nm
Total mass = 472000 N
total moment = 7204000Nm

New CG = moment / Mass
= 7204000 / 472000
= 15.26m

LEMac is at 14m therefore CG is 1.26m from LEMac

As a %MAC then:
1.26/4.6 x 100 = 27.5%MAC.