A., S., P., D., N., W.(1989).Economics / Paul A. Samuelson, William D. Nordhaus (Ed.ke-13).New York:McGraw-Hill book company.
Gaya MLA
Samuelson, Paul, A.., Nordhaus, William, D.."Economics / Paul A. Samuelson, William D. Nordhaus".Ed.ke-13New York:McGraw-Hill book company,1989.Textbook.