The correct transformation of $g(x) = f(-x) + 3$ can be described as follows:

1. Reflection across the y-axis: The negative sign inside the function, $f(-x)$, reflects the function $f(x)$ across the y-axis.
2. Vertical translation: The $+3$ outside the function adds 3 units, which shifts the graph of $f(-x)$ vertically upward by 3 units.

Thus, the correct description is:

g(x) reflects f(x) across the y-axis and is translated 3 units upward.

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Do you want more details or have any questions? Here are some related questions to explore:

1. How do different transformations (e.g., $f(x) + c$, $f(x - c)$) affect the graph of a function?
2. What is the effect of reflecting a function across the x-axis versus the y-axis?
3. How can you identify a vertical or horizontal stretch/compression in a function transformation?
4. What happens when multiple transformations (e.g., reflection and translation) are applied to a function?
5. Can you describe the impact of a horizontal shift to the left or right on a function's graph?

Tip: When analyzing transformations, always pay attention to whether changes occur inside or outside the function to determine horizontal or vertical effects.