The formula of a midpoint:
[tex]M_{AB}\left(\dfrac{x_A+x_B}{2},\ \dfrac{y_A+y_B}{2}\right)[/tex]
We have:
[tex]M(-6,\ 8)\to x_M=-6,\ y_M=8\\A(-2,\ 10)\to x_A=-2,\ y_A=10[/tex]
Substitute:
[tex]\dfrac{-2+x_B}{2}=-6\qquad|\cdot2\\\\-2+x_B=-12\qquad|+2\\\\x_B=-10\\\\\dfrac{10+y_B}{2}=8\qquad|\cdot2\\\\10+y_B=16\qquad|-10\\\\y_B=6[/tex]
Answer: B. (-10, 6)
