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