The average rate of change of on the interval [a,b] is:
f(b)−f(a)/ b-a
or
y1-y2/x1-x2 which is how I learned it, average ratw of change is just slope
so you would plug your numbers into x
1st the b: 6((1))^2+31((1))-12
=6+31-12 1^2=1, so it cancels
f(b) =25
2nd the a: 6((-2))^2+31((-2))-12
=6(4)+31(-2)-12
=24+-62-12
f(a) =-50
3rd plug them in: (25- -50)÷(1-(-2)
=75÷3
=25
so your average rate of change(or slope) is 25 :)