Let $f ( x ) = 6 x - e ^ { x }$

Multiple Choice

Let $f ( x ) = 6 x - e ^ { x }$ Then $f ^ { \prime } ( x ) = 0$ for all x in

A) $( - \infty , \infty )$
B) $( - \infty , \ln 6 )$
C) $( \ln 6 , \infty )$
D) $( - \infty , 6 )$
E) $( - \infty , - \ln 6 )$