If you examine the x point:
-1 became -1/5
That is , x coordinate divided by 5
If you examing the y point:
12 became 2 and 2/5, or 12/5
That is, y coordinate divided by 5
So, both the points are divided by 5, or hence, mutliplied by (1/5)th
Thus, the scale factor is:
[tex]\frac{1}{5}[/tex]