Functions $f$ and $g$ are defined on the set of real numbers as
$$\begin{aligned}& f ( x ) = \frac { x \cdot ( x - 2 ) } { 2 } \\& g ( x ) = \frac { x \cdot ( x - 1 ) \cdot ( x - 2 ) } { 3 }\end{aligned}$$
The sum of the $\mathbf{x}$ values satisfying the equality
$$f ( 2 x ) = g ( x + 1 )$$
is what?\
A) 1\
B) 3\
C) 4\
D) 6\
E) 8