The price of a phone call at a pay phone was 5 cents in 1950 and the price of a first- class stamp was 3 cents. In 2016, the pay phone costs 50 cents for a call and a first- class stamp costs 47 cents. We know that both the nominal prices of phone calls and first-class stamps increased from 1950 to 2016, but we can't tell if the relative prices increased or decreased without more information. both the nominal prices of phone calls and first-class stamps increased from 1950 to 2016, but the relative price of stamps increased and the relative price of phone calls decreased from 1950 to 2016. all prices increased from 1950 to 2016: Nominal prices of phone calls, first-class stamps, and the relative prices of phone calls and first-class stamps. both the nominal and the relative price of phone calls increased from 1950 to 2016.