Avg = [(x+3)^2 + (x-3)^2] / 2
Expanding and simplifying, (x^2 + 6x + 9 + x^2 - 6x + 9 ) / 2 = x^2 + 9
Which of the following is equal to the average (arithmetic mean) of (x+3)^2 and (x-3)^2?

(a) x^2
(b) x^2+2
(c) x^2 +4
(d) x^2+9
(e) x^2+4x