The population doubled by 1978, and the population growth rate peaked at 3.4% in 1985. At the 2006 census, the population had reached 298,968, although the census in 2000 showed that the population growth rate had declined to 1.9%. Life expectancy at birth stood at 46 years in 1978, and later rose to 72. Infant mortality has declined from 12.7% in 1977 to 1.2% today, and adult literacy reached 99%. Combined school enrolment reached the high 90s. The population was projected to have reached 317,280 in 2010.. How many years did the life expectancy increase by?