For the Given Functions F and G, Find the Requested $$f ( x ) = 7 x + 3 ; g ( x ) = 3 x + 7$$

For the given functions f and g, find the requested function and state its domain.
- $$f ( x ) = 7 x + 3 ; g ( x ) = 3 x + 7$$
Find f $\cdot g .$

A) $( f \cdot g ) ( x ) = 21 x ^ { 2 } + 21 ; \{ x \mid x \neq 21 \}$
B) $( f \cdot g ) ( x ) = 21 x ^ { 2 } + 58 x + 21$ ; all real numbers
C) $( f \cdot g ) ( x ) = 10 x ^ { 2 } + 58 x + 10$ ; all real numbers
D) $( f \cdot g ) ( x ) = 21 x ^ { 2 } + 16 x + 21 ; \{ x \mid x \neq 21 \}$