A function $f$ is even if it satisfies $f(x) = f(-x)$ for all $x$ in its domain. An example of an even function is $f(x) = x^2$ since $(x^2) = (-x)^2$.
$f$ is odd if it satisfies $f(x) = -f(-x)$ for all $x$ in its domain. An example of an odd function is $f(x) = x^3$ since $x^3 = -(-x)^3.$
Functions may be neither even nor odd, for example the function $f(x) = x^2+x^3$ is in that category. For each function below enter the letter E if the function is even, the letter O (not the digit $0$!) if it's odd, and the letter N if it's neither even nor odd.
$f(x) = x^4.$
$f(x) = x^5.$
$f(x) = x^4 + x^5.$