2x+5y= 3 -x+ 3y= -7 using elimination

2x + 5y = 3
-x + 3y = -7

multiply the second equation by 2
-2x + 6y = -14

2x + 5y = 3
-2x + 6y = -14

add two equations
        2x + 5y = 3
+     -2x + 6y = -14

11y = -11
y= -1

substitute -1 to any of the equations
2x + 5(-1) = 3
2x - 5 = 3
2x = 8
x = 4

so the final answers are..
x = 4 , y = -1

E(5,5;5)

E is midpoint of A and C, B and D