MLA

Berberova, N. (Nina), 1901-1993. Kellar, Suzanne. Box 11, folder 285. n.d.. https://collections.library.yale.edu/catalog/16688003.

APA, 6th edition

Berberova, N. (Nina), 1901-1993. (["Box 11, folder 285"])(n.d.)[Kellar, Suzanne]. https://collections.library.yale.edu/catalog/16688003.