MLA

Kilpatrick, Jack Frederick (1915-1967). Duncan, Walter. Letter to Dollie Duncan on Oklahoma State Penitentiary stationary. Box 22, folder 1844. 1951 February 7. https://collections.library.yale.edu/catalog/15532648.

APA, 6th edition

Kilpatrick, Jack Frederick (1915-1967). (["Box 22, folder 1844"])(1951 February 7)[Duncan, Walter. Letter to Dollie Duncan on Oklahoma State Penitentiary stationary]. https://collections.library.yale.edu/catalog/15532648.