MLA

Wolff, Helen, 1906-1994. Stern, Fritz [Richard?]. Box 41, folder 1284. 1985 May 3. https://collections.library.yale.edu/catalog/17269616.

APA, 6th edition

Wolff, Helen, 1906-1994. (["Box 41, folder 1284"])(1985 May 3)[Stern, Fritz [Richard?]]. https://collections.library.yale.edu/catalog/17269616.