Charlie
Here, we want to check if polynomials is closed under subtraction or not
To check this, we proceed either ways, if the answer is same, then it is closed. If otherwise, then it is not
We have;
[tex]\begin{gathered} 5x^2-9x^2=-4x^2 \\ \\ \text{And;} \\ \\ 9x^2-5x^2=4x^2 \end{gathered}[/tex]As we can see, both results are not equal
If subtraction was closed under polynomials, then the results of both should have been equal. This means Charlie is correct.