Solve the Problem $f ( x ) = \sqrt { x ^ { 2 } - 9 x + 45 } - 1$

Multiple Choice

Solve the problem.
-For the function $f ( x ) = \sqrt { x ^ { 2 } - 9 x + 45 } - 1$ , find all values $x$ for which $f ( x ) = 4$ .

A) $\{ 5,4 \}$
B) $\{ 5 , - 4 \}$
C) $\{ - 5 , - 4 \}$
D) $\varnothing$