Question

Construct a cubic polynomial with real coefficients, one of whose zeros is 6 + i, and passing through the point (-1,20).

Answer 1

If it is a polynomial with real coefficients, that means your complex root has a partner, it's conjugate, which is 6-i. This will create a quadratic.

Answer 2

Now as @calmat01 has said, U now know two roots form a cubic polynomial\[ax ^{3}+b ^{2}+cx+d=0\]
and find the other root