Using Value in Cell to hide/unhide rows

I manage to make some progress. I used the following codes to perform the function

Sub HIDEROWUSINGTEXT()
If Range("A9").Value = 5 Then
Rows("7:7").EntireRow.Hidden = True
Else
Rows("7:7").EntireRow.Hidden = False
End If
End Sub

By having a value 5 in cell A9 and when i ran the macro, row 7 got hidden. However, i had to run the marco everytime i change the value in the cell. Maybe if anyone can help me modify the codes to hide/unhide row 7 every time i change it would be good...