How to merger two functions into one function?

There are many repeat code in the two functions, could you tell me how to  merger two functions into one function?
Thanks!
 
        public static void AddClientURLForButton(Button myButton, string fileName,string size)
        {
            myButton.OnClientClick = "return window.open('" + fileName + "','WindowName" + DateTime.Now.Millisecond.ToString() + "'," + size + ");";
        }

        public static void AddClientURLForLinkButton(ImageButton aImageButton, string fileName,string size)
        {
            aImageButton.OnClientClick = "return window.open('&quo ...