MLA

Brodsky, Joseph, 1940-1996. Dovlatov, Sergei. Box 4, folder 112. undated. https://collections.library.yale.edu/catalog/10051161.

APA, 6th edition

Brodsky, Joseph, 1940-1996. (["Box 4, folder 112"])(undated)[Dovlatov, Sergei]. https://collections.library.yale.edu/catalog/10051161.