MLA

Dunbar, Rudolph, 1899-1988. King, Coretta Scott. Box 1, folder 20. 1968. https://collections.library.yale.edu/catalog/17029231.

APA, 6th edition

Dunbar, Rudolph, 1899-1988. (["Box 1, folder 20"])(1968)[King, Coretta Scott]. https://collections.library.yale.edu/catalog/17029231.