I believe the answer they're looking for is 3, but it's hard to tell, because there's a negative sign before the box, and a polynomial cannot contain a negative exponent.
Ignoring that sign though, the answer should be 3 because Polynomials typically have a term with each degree up to the maximum of the polynomial.
In this polynomial, there is a term with degree 4, degree 2, and degree 0, but none for degree 3 or 1. Because of this, the only acceptable answer is 3.