Which represents “if x=4, then y=-2”

You haven't shared the answer choices.

Still, we could invent a function for which the above statement is true:

y = mx + b, and "if x = 4, y = -2" becomes -2 = m(4) + b.  Unfortunately, we have 2 unknowns here.  

If we arbirtrarily let b = 3, then y = mx + b becomes y = mx + 3.  Subst. 4 for x and -2 for y, we get      -2 = m(4) + 3, or -5 = 4m, or m = -5/4.

Then y = mx + b   becomes    y = (-5/4)x + 3.  (this is just an example!!!)