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Algebra 2a Help?

What is the average rate of change of f(x), represented by the graph, over the interval [-1, 2]?

a. -2.5
b. -2
c. 2.5
d. 3
e. 6

Help would be much appreciated !!!

[f(2)-f(-1)]/[2--1] = (2.5--5)/(3)
= 7.5/3 = 2.5

However this interval contains two discontinuities so the value does not mean much.