I believe your interval is [-2,2]: all numbers between -2 and +2.
Then the ave. r. of c. on this interval is:
f(2) - f(-2) 4^2 + 2 - {4^(-2) + 2}
------------- = ------------------------------
2 - (-2) 4
16 - (1/16) 15 15/16
= --------------------- = --------------- = 3.98 or 255/64
4 4
