Chinas trend growth rate of real GDP per person was 2.2 percent a year before 1980 and

Question:

China’s trend growth rate of real GDP per person was 2.2 percent a year before 1980 and 8.7 percent a year after 1980. In the year to August 2009, China’s output increased by 11.3 percent.
Distinguish between a rise in China’s economic growth rate and a temporary cyclical expansion. How long, at the current growth rate, will it take for China to double its real GDP per person?