Answer
$1/8$ *8 +$1/2$*6
Work Step by Step
Copper has FCC Latice structure and each unit cell of copper has 8 atoms at 8 corners of each cell and 6 atoms at 6 faces of Cubic cell structure.
The each atom at corner of cube is shared by 8 adjacent cells and therefore each atom contributes only 1/8 to each cell and 8 atoms contribute (1/8*8)=1
The each atom at face of cubic unit cell is shared by the adjacent similar unit cell in lattice therefore each atom contributes only 1/2 to each unit cell and 6 atoms contribute 6*1/2 = 3 atoms to each cell .
Total number of atoms in unit cell of copper are
1+3 =4 unit cells
