The population of Cirque City was 46,229 in 1999 and was 55,680 in 2010. If the population was growing exponentially, what will the population be in2020?

Start by subtracting 46,229 from 55,680 = 9,451 total growth.  

Presuming the growth is a constant of the average: divide 9,451 / 11 = 859.18 growth per year.  (2010 - 1999 = 11 years)

859.18 x 10 = 8,591 total growth ---- 2020 - 2010 = 10 years 

Population in 2010 = 55,680 + 8,591 = 64,271 total population in 2020

Exponentially just means quickly.