6. Given the following two equations in $x$: $6(x+8)=18 x ; 6 x-2(a-x)=2 a+x$ have the same solution, then $a=(\quad)$
【Analysis】
$$
\begin{aligned}
6(x+8) & =18 x \\
6 x+48 & =18 x \\
12 x & =48 \\
x & =4
\end{aligned}
$$

Substitute into the second equation, solve the equation
$$
\begin{aligned}
6 \times 4-2(a-4) & =2 a+4 \\
24-2 a+8 & =2 a+4 \\
4 a & =28 \\
a & =7
\end{aligned}
$$