William, S., A., S., P.(1980).Economics / Paul A. Samuelson, William Samuelson (Ed.ke-7).:McGraw-Hill International Book Company.
Gaya MLA
Samuelson, William., Samuelson, Paul, A.."Economics / Paul A. Samuelson, William Samuelson".Ed.ke-7:McGraw-Hill International Book Company,1980.Textbook.