The country's population in 1992 was 28 million in 1999 it was 30 million estimated population in 2008

Between 1992 and 1999 there are 7 years: the population rose 2 million in 7 years or 2/7 million each year.

Between 1999 and 2008 there are 9 years.  Each year the population would rise 2/7 million so over 9 years that would be 18/7 or approimately 2 1/2 million

Therefore the estimated population would be 30 + 2 1/2 = 32 1/2 million