Let f(x)=x2−2x−4 . what is the average rate of change for the quadratic function from x=−1 to x = 4?

The average rate of change x=−1 to x = 4 is 

A= f(4) -f(-1) / 4- (-1)
f(4)=4²-2x4-4=16-12=4
f(-1)=1+2-4= -1
f(4) -f(-1) / 4- (-1) = 4-(-1)/4-(-1)= 5/5=1
the rate of change is A=1