MLA

Hughes, Langston, 1902-1967. Peterson, Dorothy. Box 20, folder 287. 1875, 1931, undated. https://collections.library.yale.edu/catalog/16207064.

APA, 6th edition

Hughes, Langston, 1902-1967. (["Box 20, folder 287"])(1875, 1931, undated)[Peterson, Dorothy]. https://collections.library.yale.edu/catalog/16207064.