MLA

Campbell, Gladys, 1892-1992. Roberts, Elizabeth Madox. Box 2, folder 46. 1936. https://collections.library.yale.edu/catalog/17209858.

APA, 6th edition

Campbell, Gladys, 1892-1992. (["Box 2, folder 46"])(1936)[Roberts, Elizabeth Madox]. https://collections.library.yale.edu/catalog/17209858.