MLA

Koch, Frederick R. (Frederick Robinson). Music/Macbeth. Box 209, folder 1551. [1941-42]. https://collections.library.yale.edu/catalog/2067978.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 209, folder 1551"])([1941-42])[Music/Macbeth]. https://collections.library.yale.edu/catalog/2067978.