Question

A line segment XY has an endpoint and the midpoint is ..? (3,0) - X (8,5)- M. What are the coordinates of the endpoint Y?

Answer 1

no idea what (3,0) - X (8,5)- M.
is supposed to say

I will assume one end point is X(8,5) and the midpoint is M(3,0)

let the other endpoint be Y(a,b)

for the x's :
(a+8)/2 = 3
a+8 = 6
x = -2

for the y's
(b+5)/2 = 0
b+5=0
b= -5

the other endpoint is Y(-2, -5)

If that is not what you meant, make the necessary changes, by
following my method. The method is correct

Answer 2

Looks to me more like (3,0) - X (8,5)- M means
X = (3,0) and M = (8,5)
That makes Y = (13,10)