For fcc, rank of the unit cell (Z)=4
Mass of one Cu-atom, M=63.55u
Avogadro's number, NA​=6.023×1023 atom
Edge length, a=xA˚=x×10−8 cm
density (d)=NA​×a3Z×M​
=6.023×1023×(x×10−8)34×63.55​
=x3422.048​ g cm−3