Complex sentence: Baer built Hazlitt into "a world-class concern", and in 1973, a merger created Hazlitt, Gooden & Fox, opening a New York affiliate gallery.
Split into simpler sentences: Baer built Hazlitt into "a world-class concern". In 1973, a merger created Hazlitt, Gooden & Fox, followed by the opening of a New York affiliate gallery.