Final answer:
The formula for the number of people P in year t is P(t) = 550 x (1 - 1/4)^t.
Step-by-step explanation:
The formula for the number of people P in year t can be given as:
P(t) = 550 x (1 - 1/4)^t
Here, P(t) represents the number of people in year t, 1/4 represents one-fourth of the remaining population leaving each year, and t represents the number of years that have passed since the mill closed.
Learn more about Population decline