How can simplify the nested if condition in excel formula

The excel formula is,

=IF(OR(B42="First Proof",B42="Revised First Proof"),IF(WEEKDAY(J42-1)=1,J42-2,J42-1),IF(OR(B42="Revises2",B42="Revises3",B42="Revises4",B42="Revises5",B42="Revises6",B42="Revises7"),IF(WEEKDAY(Q42-1)=1,Q42-2,Q42*1),IF(B42="Revises1",IF(WEEKDAY(J42-1)=1,J42-2,J42-1),IF(B42="Typescript",IF(WEEKDAY(J42-1)=1,J42-2,J42-1),IF(B42="Finals",IF(WEEKDAY(J42-1)=1,J42-2,J42-1),IF(OR(B42="ELDs",B42="Post Conversion",B42="Revised ELDs"),"NA"))))))

Please help me to reduce the formula length.