Private Sub Worksheet_Change(ByVal Target As Range)
Dim i As Long, SumMonth As Double, SumYear As Double
    If Not Intersect(Target, Range("A2:A35")) Is Nothing Then
        Application.EnableEvents = False
        For i = 2 To 35
            If Cells(i, 1) = "a" Then
                SumMonth = SumMonth + Cells(i, 4)
                SumYear = SumYear + Cells(i, 6)
            End If
        Next
    End If
    Cells(36, 6) = SumMonth
    Cells(41, 6) = SumYear
    Application.EnableEvents = True
End Sub