MLA

Kilpatrick, Jack Frederick (1915-1967). Business letter. Box 6, folder 514. 1925 April 3. https://collections.library.yale.edu/catalog/15492654.

APA, 6th edition

Kilpatrick, Jack Frederick (1915-1967). (["Box 6, folder 514"])(1925 April 3)[Business letter]. https://collections.library.yale.edu/catalog/15492654.