Respuesta :
Count the distance in x and y separately from B to X
12 -> 3 = 9 (subtracted) , -7 -> -1 = 6 (added).
X is midpnt, so if we go from B to X, we must go from X to get A.
subtract another 9 from the x value, and add another 6 to the y value of X
That gives us -6, 5, which are the coordinates of A.
