For the function [tex]\( f(x) = \left| x^2 - 4x + 8 \right| \)[/tex], complete parts (a)-(d) below.
(a) Evaluate [tex]\( f(6) \)[/tex]. Select the correct choice below and, if necessary, fill in the answer box to complete your choice.
A. [tex]\( f(6) = \ \square \)[/tex] (Simplify your answer.)
B. [tex]\( f(6) \)[/tex] is undefined.