Gaya APA

Ruffin, R, J., Gregory, P, R. (1988). Principles of Economics Ed. 3 (Ke-3). Amerika: Scott, Foresman and Company.

Gaya MLA

Ruffin, Roy, J.., Gregory, Paul, R.. "Principles of Economics Ed. 3". Ke-3 Amerika: Scott, Foresman and Company, 1988. Text.