The midpoint of a line segment with end points as (-10, y1) and (-6, 7) is (-8, 6). what is the value of y1? midpoint formula is (x1 + x2)/2 , (y1 + y2)/2 but i keep getting a wrong answer.,

The formulae for the midpoint are correct:

M ( (x₂-x₁)/2 , (y₂-y₁)/2 )

You need to invert these to get x₁ and y₁:
x₁ =2xm - x₂
y₁ =2ym - y₂

Try with the x to prove the formulae are correct:
x₁ =2·(-8) - (-6) = -16 + 6 = -10  which is what we have!

Then, use the other formula for y:
y₁ =2 ·(6) - (7) = 12 - 7 = 5

Therefore y₁ = 5

D.