Answer
polynomial, $n=3$,
$f(x)=x^3+4x$, $x^3$ , $0$.
Work Step by Step
Step 1. Given $f(x)=4x+x^3$, we can determine it is a polynomial function.
Step 2. We can identify the degree as $n=3$.
Step 3. In standard form $f(x)=x^3+4x$. We can identify the leading term as $x^3$ and the constant term as $0$.