What kind of transformation converts the graph of $f(x)=-3 x-2$ into the graph of $g(x)=$ $3 x-2$ ? horizontal stretch horizontal shrink reflection across the $x$-axis reflection across the $y$-axis

Step 1 ：The function $f(x)=-3 x-2$ and $g(x)=3 x-2$ are linear functions.

Step 2 ：The only difference between them is the sign of the coefficient of $x$.

Step 3 ：This means that the graph of $f(x)$ is a reflection of the graph of $g(x)$ across the x-axis.

Step 4 ：Therefore, the transformation that converts the graph of $f(x)$ into the graph of $g(x)$ is a reflection across the x-axis.

Step 5 ：\(\boxed{\text{reflection across the x-axis}}\)