Answer: Choice B
7200+80x = 3200+120x
Reason:
Canton starts off with 7200 people. Add on 80x to represent the fact the town grows 80 people per year. That's how we end up with the expression of 7200+80x
Similarly, the expression 3200+120x represents the idea Holly Springs started off with 3200 people and grows at 120 people per year.