I need some help and clarification with a math problem...please help!!?

So here is the entire question from start to finish: A census study shows that the population from 1990 to 1998 of the only large town in a certain county can be modeled by the formula 102t^2-225t+3090 where t=0 represents the year 1990 and that over the same years, the population of the surrounding county (not including the town) can be modeled by the formula 125t^2+72t+4978 where t=0 represents the year 1990. Find a model for the total population of the county during the years 1990 to 1997.