How to write a program using visual studios that will calculate the population growth between two given years?

SOURCE: use Casio fx570ms to calculate growth rate between two periods

Usually, population changes are not linear, but since you give only two points (2000, 206 000) and (2010, 240 000) that is all you can calculate. The average growth rate is given by the rise over run.
Growth Rate=(240 000-206 000)/(2010-2000)=34 000/10