It is a root of the polynomial if it causes the equation to equal 0.
Let's try each number.
Substituting -3 for x...
(-3)³ - 4(-3)² -11(-3) + 30
-27 - 36 + 33 + 30
0
Therefore, a. -3 is a root to our polynomial.
You could try the rest, but I won't waste time with it. None of the others are roots, and it's multiple choice which means usually just one answer.