Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Address = "$B$2" Then
If Target = "" Then Cells.EntireRow.Hidden = False: Exit Sub
Application.ScreenUpdating = False
Cells.EntireRow.Hidden = False
Range(Cells((Target * 3) + 6, 1), Cells([C65000].End(xlUp).Row, 1)).EntireRow.Hidden = True
End If
End Sub