MLA

Ferro, Robert (1941-1988). Grumley, Michael. Box 1, folder 10. 1978-1987, undated. https://collections.library.yale.edu/catalog/17099440.

APA, 6th edition

Ferro, Robert (1941-1988). (["Box 1, folder 10"])(1978-1987, undated)[Grumley, Michael]. https://collections.library.yale.edu/catalog/17099440.