Ok so
-10, -6
4,-6
-3,-13
-3,1
should be it
First of all, a positive average rate of change means that the function is increasing, so the answer can only be A->B or B->C.
The average rate of change is defined as

i.e. as the ratio between the vertical and horizontal gain.
In order to go from point A to point B, you gain 1 unit horizontally and 5 units vertically. So, the average rate of change is 5/1=5.
In order to go from point B to point C, you gain 1 unit horizontally and 3 units vertically. So, the average rate of change is 3/1=3.
Answer:
-2a + 3
Step-by-step explanation:
We can substitute a + 7 for x:
f(a + 7) = 17 - 2(a+7) = 17 - 2a - 14 = -2a + 3