Sub test()
Dim cellule As Range, cellule1 As Range, cellule2 As Range, resultat As Range
For Each cellule In Range(Range("c5"), Range("c5").End(xlDown))
If cellule.EntireRow.Hidden = False Then
Set cellule1 = cellule.Offset(0, -1)
For ligne = cellule1.Row To 5 Step -1
If Cells(ligne, cellule1.Column).EntireRow.Hidden = False Then
Set cellule2 = Cells(ligne - 1, cellule1.Column)
Exit For
End If
Next
cellule.Value = cellule1 * cellule2
End If
Next
End Sub