f(x) = x^3 + x^2 + 3x^0 is neither even nor odd. Why? Because we have a mixture of even and odd powers of x here: x^3 (odd) and x^2 and x^0 (even).
Even functions: all component functions are even (e. g., x^2 and x^0).
Odd functions: all component functions are odd (e. g., x^5 and x^3.
Neither: There's a mixture of even ad odd functions.
Another way to test for even, odd or neither:
Even functions: f(-x) = f(x). Changing the sign of the input (x) doesn't change the sign of the output.
Odd functions: f(-x) = -f(x). Changing the sign of the input changes the sign of the output.