MLA

Baldwin, James, 1924-1987. "An Open Letter to My Sister, Angela Y. Davis". Box 1, folder GROUP 4, F-12. 1970 November 19. https://collections.library.yale.edu/catalog/17246522.

APA, 6th edition

Baldwin, James, 1924-1987. (["Box 1, folder GROUP 4, F-12"])(1970 November 19)["An Open Letter to My Sister, Angela Y. Davis"]. https://collections.library.yale.edu/catalog/17246522.