Final answer:
The formula for the population at time t can be determined by subtracting the decrease from the initial population for (a) and using exponential decay for (b).
Step-by-step explanation:
(a) If the population decreases by 100 people per year, the formula for the population, P, at time t can be determined as:
P = 5000 - 100t
(b) If the population decreases by 8% per year, the formula for the population, P, at time t can be determined as:
P = 5000(1 - 0.08)^t