MLA

Wilder, Thornton, 1897-1975. Wilder, Charlotte. Box 3, folder 71-74. 1916-71, n.d.. https://collections.library.yale.edu/catalog/16587314.

APA, 6th edition

Wilder, Thornton, 1897-1975. (["Box 3, folder 71-74"])(1916-71, n.d.)[Wilder, Charlotte]. https://collections.library.yale.edu/catalog/16587314.