The MOD function gives you the whole number remainder after dividing.
For an example, put this into a blank module and run it:
Public Sub Test1()
MsgBox (32 Mod 9), vbExclamation
End Sub
The message box will return 5 (32/9 = 3.555555 but 32-27=5 which is the whole number remainder after dividing 32 by 9)