MLA

Coffin, William Sloane, Jr., 1924-2006. William Sloane Coffin. Box 18, folder 3. Undated. https://collections.library.yale.edu/catalog/10015353.

APA, 6th edition

Coffin, William Sloane, Jr., 1924-2006. (["Box 18, folder 3"])(Undated)[William Sloane Coffin]. https://collections.library.yale.edu/catalog/10015353.