If you look at 10 newspapers per 20 minutes, you can divide newspapers by minutes which gives you 10/20 = 1 newspaper per 2 minutes. To check the answer, you can do 2*30=60 since 2 minutes per each newspaper would equal 60 minutes.
This is (y2-y1)/(x2-x1), y2 being 12, y1 being 7, x2 being -39 and x1 being 26. So if you plug in the points it would be: (12-7)/(-39-26). This solved equals: -5/65 which simplified equals: -1/13
