MLA

Williams, William Carlos, 1883-1963. Brown, Bob. Box 3, folder 83. 1930-1950, undated. https://collections.library.yale.edu/catalog/11870017.

APA, 6th edition

Williams, William Carlos, 1883-1963. (["Box 3, folder 83"])(1930-1950, undated)[Brown, Bob]. https://collections.library.yale.edu/catalog/11870017.