The answer is C.
Steps:
Rewrite Problem
Change all signs in the second parenthesis to the opposite sign
Combine Like Terms
The main thing about a polynomial is it's the sum of terms, each a constant coefficient times whole number power (0, 1, 2, 3, ...) of the variable.
A. 35x² is a polynomial; the power 2 is a whole number. There's only one term so not really the sum of terms, but one's enough.
B. 
That's a perfectly good polynomial but you might not have gotten to it in algebra I yet. The square root of negative 1 is abbreviated <em>i</em> and when we add it to the set of real numbers we get complex numbers. It has a complex coefficient 4+i but that's OK in a polynomial.
If you haven't gotten to complex numbers yet you might be expected to answer no to this one. I don't know.
C. 
The negative exponent means this isn't a polynomial.
D. x/5 + 2
That's fine, just another way of writing

which is a perfectly ok polynomial.
Answer: A B D
It takes Cayson 2.5 hours to get from house to the stadium and it takes Riley 3 hours to get from house to the lake. In total they spent 5.5 hours to overcome the distance 385 mi.
Use formula:
where D is distance, r - speed and t - time.
Thus,
mi/h.
Answer: 70 mi/h.
-2 would be the coefficient of the y-term