Perform the Requested Operation or Operations $f ( x ) = \sqrt { 6 x + 6 } , g ( x ) = \sqrt { 6 x - 6 }$

Multiple Choice

Perform the requested operation or operations. Find the domain of each.
- $f ( x ) = \sqrt { 6 x + 6 } , g ( x ) = \sqrt { 6 x - 6 }$ Find $( f + g ) ( x )$

A) $\sqrt { 12 x }$ ; domain: $[ 0 , \infty )$
B) $x \sqrt { 12 }$ ; domain: $( - \infty , \infty )$
C) $6 x$ ; domain: $( - \infty , \infty )$
D) $\sqrt { 6 x + 6 } + \sqrt { 6 x - 6 }$ ; domain: $[ 1 , \infty )$