The Derivative Of $f ( x ) = \sqrt { x - 4 }$

Multiple Choice

The derivative of $f ( x ) = \sqrt { x - 4 }$ at x = 8 is

A) $- \frac { 1 } { 8 }$
B) $- \frac { 1 } { 4 }$
C) $- \frac { 1 } { 2 }$
D) $\frac { 1 } { 4 }$
E) $\frac { 1 } { 8 }$