MLA

Kuh, Katharine, 1904-1994. Kopman, Benjamin. Box 1, folder 14. 1937 Apr 2. https://collections.library.yale.edu/catalog/17059900.

APA, 6th edition

Kuh, Katharine, 1904-1994. (["Box 1, folder 14"])(1937 Apr 2)[Kopman, Benjamin]. https://collections.library.yale.edu/catalog/17059900.