Option Explicit
Sub OrtalamaBul()
    Dim ws As Worksheet, i As Long, adet As Long
    Dim sehir As String, urun As String
    Dim toplam As Double, tutar As Variant
    Set ws = ThisWorkbook.Worksheets("Ornek")
    sehir = Trim$(CStr(ws.Range("F4").Value2))
    urun = Trim$(CStr(ws.Range("F5").Value2))
    ws.Range("F8").ClearContents
    If sehir = "" Or urun = "" Then
        ws.Range("F8").Value = "Iki kosulu da girin"
        Exit Sub
    End If
    For i = 5 To 10
        If StrComp(Trim$(CStr(ws.Cells(i, 1).Value2)), sehir, vbTextCompare) = 0 And _
           StrComp(Trim$(CStr(ws.Cells(i, 2).Value2)), urun, vbTextCompare) = 0 Then
            tutar = ws.Cells(i, 3).Value2
            If IsError(tutar) Then
                ws.Range("F8").Value = "Tutar hatali"
                Exit Sub
            End If
            If Len(CStr(tutar)) = 0 Or Not IsNumeric(tutar) Then
                ws.Range("F8").Value = "Sayisal tutar girin"
                Exit Sub
            End If
            toplam = toplam + CDbl(tutar)
            adet = adet + 1
        End If
    Next i
    If adet = 0 Then
        ws.Range("F8").Value = "Eslesen kayit yok"
    Else
        ws.Range("F8").Value = toplam / adet
    End If
End Sub