deducting holiday from a query in a form

[shod90]

Dear All,
I have a query which have a total days of holidays and i need to show that in a form which tell the user you have how many days remaining out of 21 days.
How could it be done ?
I already gave initial value for holidays textbox as

Dim holidayDefault As Integer
holidaysDefault = 21
Me.HolidayBox.Value = holidaysDefault

how can i minus the number in that query

[June7]

Can use DLookup() expression in textbox:

=DLookup("CountOfHoliday", "queryname", "EmpID=" & [EmpID])