Answer :
[tex](18, y) \ and \ (20, -15) \ is \ (19, -5) \\ \\(x _{m},y _{m}) =[ \frac{x_{1} +x _{2}}{2} , \frac{y _{1}+y _{2}}{2}] \\ \\ (19,-5)= [\frac{20+19}{2},\frac{y-15}{2}] \\ \\(19,- 5)= [19,\frac{y-15}{2}] \\ \\ -5= \frac{y-15}{2} \ \ / *2\\ \\-10 = y-15\ \ | +15\\ \\y=-10 + 15 \\ \\ y = 5\\ \\(19,- 5)= [19,\frac{5-15}{2}] \\ \\(19,- 5)= ( 19,-5) \\ \\ \\ Aswer : y = 5[/tex]
