MLA

Wolff, Helen, 1906-1994. Hemingway, Ernest. Box 16, folder 525. 1959 Mar 23. https://collections.library.yale.edu/catalog/17269608.

APA, 6th edition

Wolff, Helen, 1906-1994. (["Box 16, folder 525"])(1959 Mar 23)[Hemingway, Ernest]. https://collections.library.yale.edu/catalog/17269608.