Question:
Suppose that $f(x)$ is a polynomial that has degree $6$ and $g(x)$ is a polynomial that has degree $3$. If $h(x)$ is also a polynomial such that $f(g(x)) + g(h(x)) + h(f(x))$ is a polynomial of degree $36$, then what is the degree of the polynomial $h$?

Answer:
Consider two arbitrary polynomials $p(x)$ and $q(x)$ with highest degree terms $x^n$ and $x^m$, respectively. Then $p(q(x)) = (q(x))^n + \cdots = (x^m + \cdots)^n + \cdots = x^{mn} + \cdots$ is a polynomial of degree $mn$. It follows that $f(g(x))$ is a polynomial of degree $18$. Then, either $g(h(x))$ or $h(f(x))$ must be a polynomial of degree $36$. This gives that the degree of $h(x)$ is either $12$ or $6$, but in the former case, the degree of $h(f(x))$ would be $72$. Thus, the degree of $h$ is $\boxed{6}$.