MLA

Carson, Rachel, 1907-1964. Robert Hines. Box 109, folder 2100. n.d.. https://collections.library.yale.edu/catalog/10191701.

APA, 6th edition

Carson, Rachel, 1907-1964. (["Box 109, folder 2100"])(n.d.)[Robert Hines]. https://collections.library.yale.edu/catalog/10191701.