Function GetXlVersion() As String 
   GetXlVersion = Val(Application.Version) 
End Function 

Function TienThue(Slg, Dgia, TyleThue) As Double 
   TienThue = Slg * Dgia * TyleThue 
End Function 

Sub FillData() 
   Dim I As Long 
   MsgBox "Ban se dien cac gia tri vao A1:A100." 
   For I = 1 To 100 
      Cells(I, 1).Value = I 
   Next I 
End Sub 

Function ThueTNCN(Luong As Double, Optional Socon As Integer) As Double 
   Dim GiamTruNuoiCon As Double, MucLuong As Double, ThucLuong As Double 
   MucLuong = 9 
   GiamTruNuoiCon = 3.6 
   ThucLuong = Luong / 10 ^ 6 - MucLuong - Socon * GiamTruNuoiCon 
   Select Case ThucLuong 
   Case Is <= 0 
      ThueTNCN = 0 
   Case Is <= 5 
      ThueTNCN = ThucLuong * 0.05 
   Case Is <= 10 
      ThueTNCN = 5 * 0.05 + (ThucLuong - 5) * 0.1 
   Case Is <= 18 
      ThueTNCN = 5 * 0.05 + 5 * 0.1 + (ThucLuong - 10) * 0.15 
   Case Is <= 32 
      ThueTNCN = 5 * 0.05 + 5 * 0.1 + 8 * 0.15 + (ThucLuong - 18) * 0.2 
   Case Is <= 52 
      ThueTNCN = 5 * 0.05 + 5 * 0.1 + 8 * 0.15 + 14 * 0.2 + (ThucLuong - 32) * 0.25 
   Case Is <= 80 
      ThueTNCN = 5 * 0.05 + 5 * 0.1 + 8 * 0.15 + 14 * 0.2 + 20 * 0.25 + (ThucLuong - 52) * 0.3 
   Case Else 
      ThueTNCN = 5 * 0.05 + 5 * 0.1 + 8 * 0.15 + 14 * 0.2 + 20 * 0.25 + 28 * 0.3 + (ThucLuong - 80) * 0.35 
   End Select 
   ThueTNCN = ThueTNCN * 10 ^ 6 
End Function
