What is the missing coordinate y of the midpoint (2,y )of segment that passes through the points (x,3) and (-1,5)?

To calculate the coordinates x and y, we'll write the
equation of the segment whose endpoints are the given
points.

(xB - xA)/(x-xA) =
(yB-yA)/(y-yA)

We'll substitute the coordinates for A and
B:

(-1-x1)/(x-x1) =
(5-3)/(y-3)

(-1-x1)/(x-x1) =
2/(y-3)

We'll cross multiply and we'll
get:

2x - 2x1 = -y  + 3 - y*x1 +
3x1

We'll move all terms to the left
side:

2x - 2x1 + y - 3 + y*x1 - 3x1 =
0

We'll combine like terms:

2x
+ y(1 + x1) - 5x1 - 3 = 0

We know that (2,y) is
the midpoint of the segment:

xM =
(x1-1)/2

2= (x1-1)/2 => x1 - 1 = 4 => x1 =
5

yM = (3+5)/2

yM =
(8)/2

yM = y =
4

The missing coordinate of the midpoint of
the segment that is passing through the given points is y =
4.