MLA
Chase-Riboud, Barbara. Letter from Barbara Chase-Riboud (Paris, France) to Her Grandparents - February 27, 1964. 1964. Stuart A. Rose Manuscript, Archives, and Rare Book Library, Box 1, Folder 3. https://digital.library.emory.edu/purl/12683bk4dc-cor.
APA, 6th edition
Chase-Riboud, B. (1964). Letter from Barbara Chase-Riboud (Paris, France) to her grandparents - February 27, 1964 (Box 1, Folder 3) [Letters (correspondence)]. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/12683bk4dc-cor.
Chicago
Chase-Riboud, Barbara. “Letter from Barbara Chase-Riboud (Paris, France) to Her Grandparents - February 27, 1964.” Letters (correspondence). Barbara Chase-Riboud Papers, 1964. Box 1, Folder 3. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/12683bk4dc-cor.