how does the rate of change vary from point to point?

Question

X Y
40 32
28 16
16 12

Answer 1

(32-16)/(40-28) = 16/12 = 4/3
(16-12)/(28-16) = 4/12 = 1/3
so, it went down by 1 or, down by a factor of 1/4
Hard to predict a trend with only two points!