-3x - 18 = 0
-3x = 18
x = -6
That makes no sense what are we supposed to figure out
midpoint= (x, y)
where x=(x1 + x2)/2
y=(y1 + y2)/2
x1=-3, x2=6, y1=5, y2=-11
so x=(-3 + 6)/2= 3/2
y=(5 + -11)/2= (5-11)/2= -6/2= -3
so mid point =(3/2, -3)
hope this helps