Suppose the average population of a town has been decreasing by 115 people per year. How has the population changed over the last six years

Even though we don't know how many originally were in that town and we don't know how many are there now, we do know that there are 6 x 115 = 690 fewer people in the town now than were there 6 years ago.

wait where is the original number of people in the town to begin with? i think we need that to solve it right?