Let

be the n'the term of the sequence.
The first term of the sequence is

the second

is 8
the third term

is 4
the fourth term

is 2
the fifth term

is 1
We notice that:
i) the values of the terms are powers of 2, and decreasing:

ii) we also notice that the subscript integer of a, and the power of 2 at that term, add to 5.
thus the general term of the sequence is given by:

.
to fit the choices of the question, we can modify this formula as follows:

The average rate of change from n=1 to n=3 is defined as:


can be found using the general formula,

,
thus the average rate of change is (4-16)/2=-12/2=-6
Answer:

,
average rate of change=-6