One endpoint of a line segment has coordinates (16, 3). If the coordinates of the midpoint are (9, 6), what are the coordinates of the other endpoint?
(2, 9)
(12.5, 4.5)
(25, 9)
(9, 3)

So the first thing we do is to multiply the top equation by 3. the reason i want to do this is i notice there will be a 6y on both equations and can possibly add/subtract them. so we get 6y = -3x + 27. adding that and the second equation we get 6x = 27-15 which is 12. divide by 6 and we get 2. ∴ x = 2. substituting 2 into the first equation we get 2y = -2 + 9 which is 7. divide by 2 and we get 7/2. ∴ y = 7/2, x = 2.