#### Answer

Sign of leading coefficient: Negative
Least Possible Degree: Three

#### Work Step by Step

RECALL:
The end behavior of the graph of a polynomial function is dependent on its leading term $ax^{n}$ and its degree $n$.
(i) If the leading term's degree is even:
(a) the end behavior is up and up if the leading coefficient is positive and
(b) the end behavior is down and down if the leading coefficient is negative.
(ii) If the leading term's degree is odd:
(a) the end behavior is down and up if the leading coefficient is positive and
(b) the end behavior is up and down if the leading coefficient is negative.
The end behavior is up, down.
Therefore the sign of the leading coefficient is negative and the degree is odd.
In general, the graph of a polynomial function of degree $n(nā„1)$ has at most $nā1 $ turning points.
The graph of a polynomial function of odd degree has an even number of turning points.
The graph of a polynomial function of even degree has an odd number of turning points.
Degree 1: Zero turning points
Degree 2: One turning point
Degree 3: Zero or two turning points
Since there are no turning points but the graph is not linear, the least possible degree is three.
Therefore, the sign of the leading coefficient is negative and the least possible degree of the polynomial function is three.