cpi-u in 1950 was 24.1 cpi-u in 1960 was 29.6 cpi-u in 1970 was 38.8 cpi-u in 1980 was 82.4 cpi-u in 1990 was 130.7 cpi-u in 2000 was 172.2 which of the 5 decades (1950s, 1960s, 1970s, 1980s, 1990s) experienced the highest level of inflation?