returning a working date

[alvinchang]

I have a future date with 10 free days given and I need a plan date based on future date -(minus) 10 free days but the returning plan date must in working day.

[#2]

In the counting of days, the first day is excluded while the last day is included, such that in your example, 28-Apr-2019 minus 10 days = 18-Apr-2019, which is the tentative plan date. So, if the future date is in A1, the formula for the plan date in B1 is:
=WORKDAY(A1-10,
--OR(WEEKDAY(A1-10)={1,7},COUNTIF(Holidays,A1-10)>0),
Holidays)
Note that Holidays refer to the defined name of the range containing the holidays.