MLA

Johnson, James Weldon, 1871-1938. Waring, Laura Wheeler. Box 103, folder 875. undated. https://collections.library.yale.edu/catalog/2110142.

APA, 6th edition

Johnson, James Weldon, 1871-1938. (["Box 103, folder 875"])(undated)[Waring, Laura Wheeler]. https://collections.library.yale.edu/catalog/2110142.