APA

Welfling W., . (1971). Principles of economics. New York: McGraw-Hill.

Chicago

Welfling Weldon, . 1971. Principles of economics. New York: McGraw-Hill.

Harvard

Welfling W., . (1971). Principles of economics. New York: McGraw-Hill.

MLA

Welfling Weldon, . Principles of economics. New York: McGraw-Hill. 1971.