If f(x) = 2x + 3, what is f(-x)?

To find $f(-x)$, replace every $x$ in the function with $-x$: $f(-x)=2(-x)+3=-2x+3$, choice J. Only the term with $x$ changes sign; the constant $3$ stays as it is. Choice F ($2x+3$) is $f(x)$ itself, with nothing replaced. Choice H ($-2x-3$) is $-f(x)$, which negates the whole function and not only the input. Choice G ($2x-3$) flips only the constant. Note that $f(-x)\ne f(x)$ and $f(-x)\ne-f(x)$, so this function is neither even nor odd.