The country's population 1992 was 147 million in 1996 it was 153 million estimate the population in 2008

In four years the population rose 153 - 147 = 6 million or 1 1/2 million each year.

Between 2008 and 1996 there are 12 years so the population would go up by 12 x 1 / 1/2 = 18 million

153 + 18 milliion = 171 million in 2008