Atoms of an element “X” make CCP and those of an element “Y” occupy half of octahedral voids and that of element Z occupy half of tetrahedral voids. Formula of the compound would be

Atoms of element “X” make CCPNumber of atoms of ‘X’/unit cell =  8  ×  18+6  ×  12=4Number of OV = 4Number of TV = 8Number of atoms of ‘Y’ =  12 4=2Number of atoms of ‘Z’ = 12 8=4 Formula is X4Y2Z4  or   X2YZ2