MLA

Stein, Gertrude, 1874-1946. Brenner, Michael. Box 99, folder 1904. 1909-31, n.d.. https://collections.library.yale.edu/catalog/17105725.

APA, 6th edition

Stein, Gertrude, 1874-1946. (["Box 99, folder 1904"])(1909-31, n.d.)[Brenner, Michael]. https://collections.library.yale.edu/catalog/17105725.