Let $$f(x) = 6 x^4 - 2 x^2 - 7.$$ Use either the first derivative test or the second derivative test to find the following:

(A) The average of the $x$ values of all local maxima of $f$.
Note: If there are no local maxima, enter -1000.

Average of $x$ values =

(B) The average of the $x$ values of all local minima of $f$.
Note: If there are no local minima, enter -1000.

Average of $x$ values =