The graph of f is reflected across the y-axis to create the graph of g. (C)
You are basically assigning the same y-value to the opposite x-values to make g(x). So, for the point (x, 31), on f(x), x is -2, but on g(x), x is 2. Thinking about this visually, you can imagine that this represents a reflection of f across the y-axis.
(Side note: Later in math, this symmetry will be formalized so that you can find it algebraically. It's called "even" symmetry.)
