The function below shows the number of car owners f(t), in thousands, in a city in different years t:

f(t) = 1.1t2 - 2.5t + 1.5

the average rate of change of f(t) from t = 3 to t = 5 is thousand owners per year.

Average rate of change from a to b = (f(b) - f(a))/(b - a) = {[1.1(5)^2 - 2.5(5) + 1.5] - [1.1(3)^2 - 2.5(3) + 1.5]} / (5 - 3) = (16.5 - 3.9) / 2 = 12.6 / 2 = 6.3

Therefore, the average rate of change of f(t) from t = 3 to t = 5 is 6.3 thousand owners per year.