Gaya APA
Ruffin, R, J., Gregory, P, R. (1993).
Economics / Paul R. Gregory, Roy J. Ruffin .
New York:
Harper Collins.
Gaya MLA
Ruffin, Roy, J.., Gregory, Paul, R..
"Economics / Paul R. Gregory, Roy J. Ruffin".
New York:
Harper Collins,
1993.
Textbook.