Final answer:
The population of Brownville in 1980 was 720,500 people, as determined by substituting x=0 into the given population growth model y=720,500(1.022)ˣ.
Step-by-step explanation:
The population of Brownville in 1980 can be determined by using the mathematical model given for the population growth: y=720,500(1.022)ˣ, where x is the number of years since January 1980. To find the initial population in January 1980 (when x=0), we substitute 0 for x into the equation because x represents the number of years since 1980.
Doing so, we get y=720,500(1.022)0. Since any number raised to the power of 0 is 1, this simplifies to y=720,500(1) which equals 720,500. Therefore, the population of Brownville in 1980 was 720,500 people.