Cita APA (7th ed.)

Butterfield, W. H. (1951). Effective personal letters (2nd edition.). Prentice-Hall.

Cita Chicago (17th ed.)

Butterfield, William Henry. Effective Personal Letters. 2nd edition. New York: Prentice-Hall, 1951.

Cita MLA (9th ed.)

Butterfield, William Henry. Effective Personal Letters. 2nd edition. Prentice-Hall, 1951.