=IF( ISERROR(WEEKDAY("20" & LEFT(TRIM($G$8),2)&"/"& $B$1& "/" &A12)),"",WEEKDAY("20" & LEFT(TRIM($G$8),2)&"/"& $B$1 & "/" &A12))

=IF( ISERROR(WEEKDAY("20" & LEFT(TRIM($G$8),2)&"/"& $B$1& "/" &A12)),"",WEEKDAY("20" & LEFT(TRIM($G$8),2)&"/"& $B$1 & "/" &A12))