Cita APA (7th ed.)

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

Cita Chicago (17th ed.)

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

Cita MLA (9th ed.)

Butterfield, William H. Effective Personal Letters. 2nd ed. Prentice-Hall, 1951.