MLA

Haas, Robert Bartlett (1916-2010). Three letters from Edward Burns, William Baker, and Carl Van Vechten to Haas. Box 5. 1936-1985, undated. https://collections.library.yale.edu/catalog/17173425.

APA, 6th edition

Haas, Robert Bartlett (1916-2010). (["Box 5"])(1936-1985, undated)[Three letters from Edward Burns, William Baker, and Carl Van Vechten to Haas]. https://collections.library.yale.edu/catalog/17173425.