'2 of the 3 standard rates in effect during the year for a U.S. first-class letter'
15c, 18c & 20c
1981: 2 of the 3 standard rates in effect during the year for a U.S. first-class letter
2 of the 3 standard rates in effect during the year for a U.S. first-class letter
2 of the 3 standard rates in effect during the year for a U.S. first-class letter
1981
15c, 18c & 20c
1981