Find the Requested Function Value for the Given Function $f ( x ) = \sqrt { 2 x - 8 }$

Find the requested function value for the given function. Round the answer to the nearest tenth when necessary.
-If $f ( x ) = \sqrt { 2 x - 8 }$ , find the value of $f ( 7 )$ .

A) 14
B) $3.7$
C) $2.4$
D) 6