=IF((A9="A")*(P9=0)=1,"HIDE","SHOW")

Option Explicit
Sub Worksheet_Activate()

    'hide all lines
    Dim i As Long

    'finds lines. 19 denotes the S column. Change 500 to last row.
    For i = 9 To 500
        If Cells(i, 19).Value = "HIDE" Then
            'hides row
            Rows(i).EntireRow.Hidden = True
        End If
    Next

End Sub