The change in the independent variable from -1 to 2 is 3.
The corresponding change in the dep't var is f(3) - f(-1), which can be found as follows:
(3)^4 - 4x - [(-1)^4 - 4(-1)] = 8 - 5 = 3
Then the ave. r. of c. of the given function on the given interval
is 3/3, or 1.