Or in A3 use (assumed the worksheet is never used at weekends, and you have to cope with state holidays otherwise)
In case you need to take holidays also into account, you need a hidden calendar table with state holidays marked, and with a calculated column which returns the number of days to previous workday in case of holiday or weekend (p.e. for my country, this may be up to 5 days if I remember correctly), and 0 in case of workday. The formula in A3 will calculate the previous workday based on this hidden table.