How do I solve this question?

The correct answer is given by option a.

Step-by-step explanation:

Rational roots theorem:

In the rational roots theorem, we take the leading coefficient(which multiplies the term of x with the highest exponent) and the independent term(which does not multiply any value of x).

The possible roots have the format p/q, in which p are the factors of the independent term, and q are the factors of the leading coefficient.

In this question:

Leading coefficient: 3

Independent term: 15

Factors of the independent term: {1, 3, 5, 15} -> p

Factors of the leading coefficient: {1,3} -> q

Possible roots:

All possible values, positive or negative, in which p is divided by q. So

So, without the repeated terms, they are:

The correct answer is given by option a.