Help me with these. Thank you!

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

Apolynomial function has a root of –6 with multiplicity 1, a root of –2 with multiplicity 3, a root of 0 with multiplicity 2, and a root of 4 with multiplicity 3. if the function has a positive leading coefficient and is of odd degree, which statement about the graph is true?

Is this a polynomial function? i need to know asap