macro for weeknum

Hi,

I do not have basic knowledge of how macro is done, I have only use record macro or copy macros done by my colleagues.Edit them and make some tests to get the result that I need. This time, I edited the macros that I got and fortunately I got what I wanted on some parts except for putting week number in a specific column, which is column T. The basis of week numbering is column A. When I put date in column A, column T would show week number. Example: If Column A has 8/15/2013 then column T should show 33 as its corresponding week. Below is my existing macro. Appreciate your help on this.

Private Sub Worksheet_SelectionChange(ByVal Target As Excel.Range)

' Time Tracker Macro

Dim AutoTime

    AutoTime = True  'Set to false to remove automatic time stamp

    If (AutoTime And ActiveCell = "" And ActiveCell.Column > 14 And ActiveCell.Column < 16 And ActiveCell.Row > 4) Then
         ActiveCell.FormulaR1C1 = "=NOW()"
         Selection.Copy
        Selection.PasteSpecial Paste:=xlValues, Operation:=xlNone, SkipBlanks:= _
            False, Transpose:=False
            Selection.NumberFormat = "hh:mm"
            
    ElseIf (AutoTime And ActiveCell = "" And ActiveCell.Column = 1 And ActiveCell.Row > 4) Then
         ActiveCell.FormulaR1C1 = "=TODAY()"
         Selection.Copy
        Selection.PasteSpecial Paste:=xlValues, Operation:=xlNone, SkipBlanks:= _
            False, Transpose:=False
         Selection.NumberFormat = "mm/dd/yyyy"
    End If
    
    
    If (AutoTime And ActiveCell = "" And ActiveCell.Column > 15 And ActiveCell.Column < 17 And ActiveCell.Row > 4) Then
         ActiveCell.FormulaR1C1 = "=NOW()"
         Selection.Copy
        Selection.PasteSpecial Paste:=xlValues, Operation:=xlNone, SkipBlanks:= _
            False, Transpose:=False
            Selection.NumberFormat = "hh:mm"
                        
    ElseIf (AutoTime And ActiveCell = "" And ActiveCell.Column = 20 And ActiveCell.Row > 4) Then
         ActiveCell.FormulaR1C1 = "=TODAY()"
         Selection.Copy
        Selection.PasteSpecial Paste:=xlValues, Operation:=xlNone, SkipBlanks:= _
         False, Transpose:=False
         Selection.NumberFormat = "mm/dd/yyyy"
         
    End If

    ActiveCell.FormulaR1C1 = WEEKNUM (RC[-20],1)

End Sub