MLA

Johnson, James Weldon, 1871-1938. from James Weldon Johnson. Box 41, folder 21. 1912 Mar-May. https://collections.library.yale.edu/catalog/17235683.

APA, 6th edition

Johnson, James Weldon, 1871-1938. (["Box 41, folder 21"])(1912 Mar-May)[from James Weldon Johnson]. https://collections.library.yale.edu/catalog/17235683.