Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
Dim lig&, col%
With Target
If .CountLarge > 1 Then Exit Sub
lig = .Row: If lig < 7 Then Exit Sub
col = .Column: If col <> 49 And col <> 51 Then Exit Sub
If IsEmpty(.Value) Then Exit Sub
Application.EnableEvents = 0
Cells(lig, 100 - col).ClearContents
Application.EnableEvents = -1
End With
End Sub