Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Address <> "$A$2" Then Exit Sub
If Target.Value = 1 Then
Rows("12:13").Hidden = False
ElseIf Target.Value = 2 Then Rows("12:15").Hidden = False
ElseIf Target.Value = 3 Then Range("12:12,15:15").EntireRow.Hidden = False
End If
End Sub