Calculating a date based on business days?

This one may be an easy one for you guys, but I'm blanking out. 

I have a field called [Date Agency Contacted]. 

I need to calculate a follow up date based on a multiple choice field called [Follow Up Days]
and have that populate into the date - formula field [Follow up Date]

The catch is that I need it to only count business days

I have this for now ;

ToWeekdayN([Date Agency Contacted] + Days(ToNumber(Left([Follow Up Days], " "))))


Only issue is that it's not skipping weekends in the count; just making sure the last day lands on a weekday.

Any help?