By definition we have to:
A set has under an operation if performance of that operation on set members always produces a member of the same set; in this case we also say that the set is closed under the operation.
For this case we have the following polynomials:

Multiplying we have:

The product of two polynomials is also a polynomial.
Answer:
d
is a polynomial
Answer:
The line plot should have 6 dots on the 12 tick mark, 2 on 13, and 6 on 16.
It would be 39,858,075 by 2100. The population goes up by x3 every 10 years.