MLA

Braithwaite, William Stanley, 1878-1962. Upson, Julia. Box 2, folder 79-80. 1908-11, undated. https://collections.library.yale.edu/catalog/16753117.

APA, 6th edition

Braithwaite, William Stanley, 1878-1962. (["Box 2, folder 79-80"])(1908-11, undated)[Upson, Julia]. https://collections.library.yale.edu/catalog/16753117.