Gaya APA

Gregory, P, R., Ruffin, R, J, 1. (1982). Principles of economics . Glenview, ill.: Scott, Foresman and Co..

Gaya MLA

Gregory, Paul, R., Ruffin, Roy, J,, 1939. "Principles of economics". Glenview, ill.: Scott, Foresman and Co., 1982. Text.