To find the midpoint, Add the two X coordinates together then divde by two and then to the same with the Y coordinates:
X = -4 + 2 = -2 / 2 = -1
Y = 6+7 = 13/2
Midpoint = (-1,13/2)
Answer:
8. 
9. 
Step-by-step explanation:

^#8^

^#9^
23b^4+(-10b^4)
23b^4-10b^4)
13b^4