Sub Additionner()
Dim r1 As Range, r2 As Range
On Error Resume Next
Set r1 = Application.InputBox("Sélectionnez les colonnes (F à L) à additionner :", "Addition", , , , , , 8)
Set r1 = Intersect(r1.EntireColumn, [F2:L65536], ActiveSheet.UsedRange)
If r1 Is Nothing Then Exit Sub
Set r2 = Application.InputBox("Sélectionnez la colonne (R à V) du résultat :", "Addition", , , , , , 8)
Set r2 = Intersect(r2(1).EntireColumn, [R2:V65536], ActiveSheet.UsedRange)
r2 = "=SUM(" & Intersect(r1, r2(1).EntireRow).Address(0, 0, xlR1C1, , r2(1)) & ")"
r2(1).Select 'facultatif
End Sub