Calculating Public Holidays when removing and adding another from tables

Hi Excel Forum,

I have a issue where I have a list of Public Holidays (which will be hidden from view) no I have these dates being broken down to the occurrence they happen on a certain day, now my problem lies if for an instance a local area does not observe that public Holiday they can select another date (which they'll be able to add dates to) to reflect that other date not taken. So I need a formula that will minus the number occurrences it happens and calculate the number of times the new date occurs on the days.

I have attached a spreadsheet where I have said Public Holidays will be required and that there will be another day that will be taken in lieu of the holiday selected in cell F15 and I the holidays that are in table A28 down to reflect in the day calculations in row 7

Any help you are able to provide would be beneficial.