Midpoint formula:
Xm = (x2-x1)/2
Ym= (y2-y1)/2
Where
xm and ym are the midpoints (-4,24)
(x1,y1)= (3,16)
x2,y2 = x,y
Replacing:
xm= (x2-x1)/2
-4 = (x-3)/2
-4(2)= x-3
-8= x-3
-8+3 =x
x =-5
Ym= (y2-y1)/2
24 = (y-16)/2
24(2)=y-16
48 = y-16
48+16 = y
y = 64
(-5,64)