M(x, y) = ((x1 + x2)/2, (y1 + y1)/2); where (x1, y1) and (x2, y2) are the coordinates of G and H respectively.
M(4, 3) = ((5 + x2)/2, (-6 + y2)/2)
(5 + x2)/2 = 4 and (-6 + y2)/2 = 3
5 + x2 = 4 * 2 = 8 and -6 + y2 = 3 * 2 = 6
x2 = 8 - 5 = 3 and y2 = 6 + 6 = 12
x2 = 3 and y2 = 12
Therefore, the coordinates of H is (3, 12)
