Answer:
Roots: -4, 1, 5 with multiplicities 1, 2, 1.
Explanation:
You have already identified the roots of g(x). The polynomial is of even degree, so the constant in the polynomial (-20) is the product of the roots. Since the product of the roots you know is -20, the remaining root must be 1. That is, the root x=1 has multiplicity 2.
On a graph of the function — my favorite way to find real roots of higher degree polynomials — you find that the curve touches, but does not cross the x-axis at x=1. This indicates a root of even multiplicity. Since there are only 4 roots and you know three of them, the "even multiplicity" must be a multiplicity of 2.
You have not identified the meaning of "b", so we cannot tell you what it is.