MLA

Hughes, Langston, 1902-1967. Price, Leontyne. Box 20, folder 292. 1964, undated. https://collections.library.yale.edu/catalog/16207069.

APA, 6th edition

Hughes, Langston, 1902-1967. (["Box 20, folder 292"])(1964, undated)[Price, Leontyne]. https://collections.library.yale.edu/catalog/16207069.