MLA

Hughes, Langston, 1902-1967. Alexander, William. Box 4, folder 69. 1942. https://collections.library.yale.edu/catalog/32466880.

APA, 6th edition

Hughes, Langston, 1902-1967. (["Box 4, folder 69"])(1942)[Alexander, William]. https://collections.library.yale.edu/catalog/32466880.