MLA

Hughes, Langston, 1902-1967. American Youth Congress. Box 7, folder 148. 1935 Jun 18. https://collections.library.yale.edu/catalog/32585049.

APA, 6th edition

Hughes, Langston, 1902-1967. (["Box 7, folder 148"])(1935 Jun 18)[American Youth Congress]. https://collections.library.yale.edu/catalog/32585049.