What is the function of 1 to -6 2 to -9 3 to -12 4 to -15?

x +1, +2, +3, +4

y -6, -9, -12, -15

Okay, the first thing I notice is that the numbers are going down by 3 each time.

So there must be a -3*x in there somewhere.

-3*1=-3  if i subtract another 3 then the answer will be -6

-3*2=-6     -6-3=-9

-3*3=-9     -9-3=-12

-3*4=-12   -12-3=-15

I do believe I have it

y = -3x-3

It is important that you think about the logic that I have used.