Average rate of change means find the slope of the secant line. So if there is a function f(x) and you want to find the average R.O.C over the interval [a,b], it would be (f(b)-f(a))/(b-a)
1. (f(3)-f(1))/(3-1)= (0-(-2))/2= 1, so D.
2. Same concept; (8-4)/(3-1)=2, so A.
3. Again, (39-(-1))/5= 8, B.