Formule Somme dans une Sélection en VBA

For Each C In rngPlage.Cells
 
    If C Like "Total *" Then
        C.Select
        Range(Selection, Selection.End(xlUp).Offset(0, 1)).Offset(0, 16).Select
        Range("tacellule").Value = Application.WorksheetFunction.Sum(Selection)
        Exit For
    End If
Next

Sub Test_Somme()
Dim rngPlage As Range
Dim C As Range
Dim der As Long 'déclare la variable der
 
Set rngPlage = Range(Range("A1"), Range("A65000").End(xlUp))
 
For Each C In rngPlage.Cells
 
    If C Like "Total *" Then
        C.Select
        'place les formules de somme
        C.Offset(0, 16).Formula = "=sum(Q" & der + 1 & ":Q" & C.Row - 1 & ")"
        C.Offset(0, 17).Formula = "=sum(R" & der + 1 & ":R" & C.Row - 1 & ")"
        der = C.Row 'redéfinit la variable der
     End If
Next
End Sub