Solution #4

We calculate the slopes between pairs of points:

(-3,-7) to (15,4): slope = 18/11
(-3,-7) to (3,-3): slope = 6/4 = 3/2
(-3,-7) to (12,3): slope = 15/10 = 3/2

So (-3,-7), (3,-3), and (12,3) are all on a line of slope 3/2. Thus (15,4) is not on a line with the other three.