To find \( g(x) \), which is a reflection of \( f(x) = x^2 - x \) over the y-axis, we need to replace \( x \) with \( -x \) in the function \( f(x) \).
So,
\[ g(x) = f(-x) = (-x)^2 - (-x) \]
Calculating that:
\[ g(x) = x^2 + x \]
Thus, the correct response is:
\[ g(x) = x^2 + x \]