MLA

Guest, Barbara, 1920-2006. Frankenthaler, Helen. Box 14, folder 271-272. 1951 February 19-2003 November 6. https://collections.library.yale.edu/catalog/17224414.

APA, 6th edition

Guest, Barbara, 1920-2006. (["Box 14, folder 271-272"])(1951 February 19-2003 November 6)[Frankenthaler, Helen]. https://collections.library.yale.edu/catalog/17224414.