Take into account that the midpoint in between the points (x1,y1) and (x,2y,2) is given by:
xo = (x1 + x2)/2
yo = (y1 + y2)/2
in this case you have
(x1,y1) = (4,-4)
(xo,yo) = (6,-1)
by using the expression for xo and yo, you can find the values of the coordinate of point B, as follow:
xo = (x1 + x2)/2
2xo = x1 + x2
x2 = 2xo - x1
x2 = 2(6) - 4
x2 = 8
yo = (y1 + y2)/2
2yo = y1 + y2
y2 = 2yo - y1
y2 = 2(-1) - (-4)
y2 = 2
Hence, the coordinates of point B is
(xo,yo) = (8,2)
