Between 1874 and 1921, the total population of Cambodia increased from about 946,000 to 2.4 million. By 1950, it had increased to between 3,710,107 and 4,073,967, and in 1962 it had reached 5.7 million. From the 1960s until 1975, the population of Cambodia increased by about 2.2% yearly, the lowest increase in Southeast Asia. By 1975 when the Khmer Rouge took power, it was estimated at 7.3 million. Of this total an estimated one to two million reportedly died between 1975 and 1978. In 1981, the PRK gave the official population figure as nearly 6.7 million, although approximately 6.3 million to 6.4 million is probably more accurate. The average annual rate of population growth from 1978 to 1985 was 2.3% (see table 2, Appendix A). A post-Khmer Rouge baby boom pushed the population above 10 million, although growth has slowed in recent years.
Question: How many millions, according to the PRK, had the population of Cambodia decreased from 1975 to 1981?
Answer: 0.6