A Ni-Cu alloy is prepared which has a lattice constant of 0.354 nm. The maximum magnetisation of the alloy is measured as 1.25*10^6 A/m. Assuming no interactions between Ni and Cu atoms, and the magnetisation comes from the all unpaired 3d Ni electrons. Estimate the wt. % Cu in the alloy. Both Ni and Cu have a fcc structure with 4 atoms in a unit cell.