If atoms ‘A’ form ccp lattice and  atoms 'B" are located at octahedral voids and atoms ‘C’ occupies tetrahedral voids, due to Schottky defect one atom is missing from the corner and one atom is missing one of the tetrahedral void, the molecular formula of the compound is

Effective number of ‘A’ atoms = Number of atoms corners $\times \frac{1}{8}$  + Number of atoms at faces $\times \frac{1}{2}$;

Since one atom is missing from corner, 

Effective number of ‘A’ atoms $=7\times \frac{1}{8}+6\times \frac{1}{2}=\frac{7}{8}+3=\frac{31}{8}$

Number of tetrahedral voids=8

but one atom from TV is missing

Effective number of ‘C’ atoms = Number of tetrahedral voids x 1 

                                               = 7 x 1 = 7

Effective number of ‘B’ atoms = Number octahedral voids in ccp x 1 

                                               = 4 x 1

Molecule formula $=A_{\frac{31}{8}}{B}_4{C}_7=A_{31}{B}_{32}{C}_{56}$