Increasing state control over the oil sector, the RCC began a program of nationalization, starting with the expropriation of British Petroleum's share of the British Petroleum-N.B. Hunt Sahir Field in December 1971. In September 1973, it was announced that all foreign oil producers active in Libya were to be nationalized. For Gaddafi, this was an important step towards socialism. It proved an economic success; while gross domestic product had been $3.8 billion in 1969, it had risen to $13.7 billion in 1974, and $24.5 billion in 1979. In turn, the Libyans' standard of life greatly improved over the first decade of Gaddafi's administration, and by 1979 the average per-capita income was at $8,170, up from $40 in 1951; this was above the average of many industrialized countries like Italy and the U.K.

In 1979, how much did the average per capita income change for Libyans?